docs: fix the lost of external file node after rebuilding

[StinsonZhao]

Description

After adding this, someone can modify *.md, then the rebuilding by 'gatsby develop' will not break the type inference for a foreign-key field created by the plugin.

Related Issues

Fix #22127

[laurieontech]

Thanks for the PR! This is a really great change. Looking at the larger doc I'm thinking we should also make an update to item 1 in the going step by step through the code section. Namely,

Define some types for MarkdownRemark using the Schema Customization API. For `featuredImg`, [point the link extension to the correct name](https://www.gatsbyjs.org/docs/preprocessing-external-images/). Defining a field for alternative text as `featuredImgAlt` can also improve accessibility, in addition to providing context for the image if it fails to load.

Would that have helped you when you ran into the problem? Open to suggestions.

[StinsonZhao]

Thanks for the PR! This is a really great change. Looking at the larger doc I'm thinking we should also make an update to item 1 in the going step by step through the code section. Namely,

Define some types for MarkdownRemark using the Schema Customization API. For `featuredImg`, [point the link extension to the correct name](https://www.gatsbyjs.org/docs/preprocessing-external-images/). Defining a field for alternative text as `featuredImgAlt` can also improve accessibility, in addition to providing context for the image if it fails to load.

Would that have helped you when you ran into the problem? Open to suggestions.

How about this change for item 1:

Define some types for MarkdownRemark using the Schema Customization API. For featuredImg, use the from argument to point the link extension to the correct field name(with a ___NODE suffix), more details about foreign-key fields here. Defining a field for alternative text as featuredImgAlt can also improve accessibility, in addition to providing context for the image if it fails to load.

[laurieontech]

That looks great!

[laurieontech]

Suggested change

1. Define some types for MarkdownRemark using the Schema Customization API. For `featuredImg`, use the `from` argument to point the `link` extension to the correct field name(with a `___NODE` suffix), [more details about foreign-key fields here](https://www.gatsbyjs.org/docs/schema-customization/#foreign-key-fields). Defining a field for alternative text as `featuredImgAlt` can also improve accessibility, in addition to providing context for the image if it fails to load.

1. Define some types for MarkdownRemark using the Schema Customization API. For `featuredImg`, use the `from` argument to point the `link` extension to the correct field name (with a `___NODE` suffix), [more details about foreign-key fields here](https://www.gatsbyjs.org/docs/schema-customization/#foreign-key-fields). Defining a field for alternative text as `featuredImgAlt` can also improve accessibility, in addition to providing context for the image if it fails to load.

[laurieontech]

This is great! Thanks so much for tracking down the solution elsewhere in the docs and making this change to help future users :)

[StinsonZhao]

That is so kind of you. Thank you.

It's a snap to me. I'll be happy if it can really help anyone else.

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