feat(docs): adding an RSS Feed

docs/docs/adding-an-rss-feed.md

@@ -0,0 +1,139 @@
+---
+title: Adding an RSS Feed
+---
+
+## What is an RSS feed?
+
+An [RSS Feed](https://en.wikipedia.org/wiki/RSS) is a standard XML file listing a website’s content in a subscribable format, allowing readers to consume your content in news aggregators, also called feed reader apps.
+
+Think of it as a syndicated distribution channel for your site's content.
+
+## Install
+
+To generate an RSS feed, you can use the [`gatsby-plugin-feed`](/packages/gatsby-plugin-feed/) package. To install this package, run the following command:
+
+```sh
+npm install --save gatsby-plugin-feed
+```
+
+## How to use [gatsby-plugin-feed](/packages/gatsby-plugin-feed/)
+
+Once installation is complete, you can now add this plugin to your site's config file, like so:
+
+```js:title=gatsby-config.js
+module.exports = {
+  siteMetadata: {
+    siteUrl: `https://www.example.com`,
+  },
+  plugins: [`gatsby-plugin-feed`],
+}
+```
+
+Here's an example of how you could implement this plugin with Markdown, but for other sources, you will need a way to uniquely identify content--typically a URL or slug.
+
+```js:title=gatsby-node.js
+const { createFilePath } = require(`gatsby-source-filesystem`)
+
+exports.onCreateNode = ({ node, actions, getNode }) => {
+  const { createNodeField } = actions
+  // highlight-next-line
+  if (node.internal.type === `MarkdownRemark`) {
+    const value = createFilePath({ node, getNode })
+    createNodeField({
+      name: `slug`,
+      node,
+      value,
+    })
+  }
+}
+```
+
+Next run a build (`npm run build`) since the RSS feed generation will only happen for production builds. By default, the generated RSS feed path is `/rss.xml`, but the plugin exposes options to configure this default functionality.
+
+For basic setups with Markdown content like the [gatsby-starter-blog](https://github.com/gatsbyjs/gatsby-starter-blog), that's all you need! However, you can craft a custom RSS feed schema using custom code in your `gatsby-node.js` and `gatsby-config.js` files.
+
+## Customizing the RSS feed plugin
+
+Your content might not fit neatly into the blog-starter scenario, for various reasons like:
+
+- Your content isn't in Markdown so the plugin doesn't know about it
+- Your Markdown files have dates in the filenames, for which the slug URLs cause 404s
+
+The good news is you can accommodate these scenarios and more in `gatsby-config.js` and `gatsby-node.js`.
+
+To customize the default feed schema (a.k.a. structure) output by the plugin to work with your website's content, you can start with the following code:
+
+```js:title=gatsby.config.js
+module.exports = {
+  plugins: [
+    {
+      resolve: `gatsby-plugin-feed`,
+      options: {
+        query: `
+          {
+            site {
+              siteMetadata {
+                title
+                description
+                siteUrl
+                site_url: siteUrl
+              }
+            }
+          }
+        `,
+        feeds: [
+          {
+            /* highlight-start */
+            serialize: ({ query: { site, allMarkdownRemark } }) => {
+              return allMarkdownRemark.edges.map(edge => {
+                /* highlight-end */
+                return Object.assign({}, edge.node.frontmatter, {
+                  description: edge.node.excerpt,
+                  date: edge.node.frontmatter.date,
+                  url: site.siteMetadata.siteUrl + edge.node.fields.slug,
+                  guid: site.siteMetadata.siteUrl + edge.node.fields.slug,
+                  custom_elements: [{ "content:encoded": edge.node.html }],
+                })
+              })
+            },
+            query: `
+              {
+                // highlight-next-line
+                allMarkdownRemark(
+                  sort: { order: DESC, fields: [frontmatter___date] },
+                ) {
+                  edges {
+                    node {
+                      excerpt
+                      html
+                      fields { slug }
+                      frontmatter {
+                        title
+                        date
+                      }
+                    }
+                  }
+                }
+              }
+            `,
+            output: "/rss.xml",
+            title: "Your Site's RSS Feed",
+          },
+        ],
+      },
+    },
+  ],
+}
+```
+
+This snippet contains a custom `gatsby-plugin-feed` setup in `gatsby-config.js` to query metadata for your site, like its `title` and `siteUrl`. It also includes a `feeds` array with at least one object containing a GraphQL query and `serialize` method, which allows you to output a custom RSS feed structure. In this example, the RSS content comes from Markdown files sourced from your site, and queried with the key `allMarkdownRemark` and its associated filters and fields.
+
+The `output` field in your feed object allows you to customize the filename for your RSS feed, and `title` for the name of your site's RSS feed.
+
+To see your feed in action, run `gatsby build && gatsby serve` and you can then inspect the content and URLs in your RSS file at `http://localhost:9000/rss.xml`.
+
+> NOTE: if your blog has custom permalinks, such as links with or without dates in them, you may need to [customize `gatsby-node.js`](https://github.com/gatsbyjs/gatsby-starter-blog/blob/master/gatsby-node.js#L57) to output the correct URLs in your RSS feed. [Get in touch with us](/contributing/how-to-contribute/) if you need any help!
+
+## Happy blogging!
+
+With the [Gatsby feed plugin](/packages/gatsby-plugin-feed/), you can share your writing easily with people subscribed through RSS readers like Feedly or RSS Feed Reader. Now that your feed is set up, you won't really have to think about it; publish a new post, and your RSS feed will automatically update with your Gatsby build. Voilà!

docs/docs/creating-a-sitemap.md

@@ -1,8 +1,8 @@
 ---
-title: Creating a sitemap
+title: Creating a Sitemap
 ---
 
-### What is a Sitemap?
+### What is a sitemap?
 
 An [XML sitemap](https://support.google.com/webmasters/answer/156184?hl=en) lists a website’s important pages, making sure search engines (such as Google) can find and crawl them all. In effect, a sitemap helps a search engine understand your website structure.
 

packages/gatsby-plugin-feed/README.md

@@ -22,6 +22,24 @@ plugins: [
 ]
 ```
 
+Here's an example of [how you could implement](/docs/adding-an-rss-feed/) this plugin with Markdown, but for other sources, you will need a way to uniquely identify content--typically a URL or slug.
+
+```javascript:title=gatsby-node.js
+const { createFilePath } = require(`gatsby-source-filesystem`)
+
+exports.onCreateNode = ({ node, actions, getNode }) => {
+  const { createNodeField } = actions
+  if (node.internal.type === `MarkdownRemark`) {
+    const value = createFilePath({ node, getNode })
+    createNodeField({
+      name: `slug`,
+      node,
+      value,
+    })
+  }
+}
+```
+
 Above is the minimal configuration required to begin working. If you wish to
 customize the query being executed to retrieve nodes, try this: