user-guide: update contributing guides with bullet styles, and

other small improvements.

Mainly per #491 (comment)

static/docs/user-guide/contributing-documentation.md

@@ -82,7 +82,7 @@ setting up.
 
 - Visit `http://localhost:3000/` and navigate to the docs in question.
 
-## Code style guidelines
+## Doc style guidelines (for Markdown)
 
 - No trailing whitespaces are allowed.
 
@@ -97,13 +97,20 @@ setting up.
   configured. You may also run `npx prettier --write <file path(s)>` manually
   before committing changes.
 
-- **Markdown**: Using `dvc <command>` in the documentation will create a link to
-  that command automatically. No need to use `[]()` explicitly to create them.
+- Using `dvc <command>` in the documentation will create a link to that command
+  automatically. No need to use `[]()` explicitly to create them.
 
-- **Markdown**: Syntax highlighting in fenced code blocks should use the `usage`
-  and `dvc` custom languages. `usage` is employed to show `dvc help` commands
+- Bullet lists shouldn't be too long, nor each bullet's text (3 sentence
+  paragraphs max.) The bullets can begin in lower case and have no ending
+  punctuation if they're not full sentences (otherwise end with period `.`). The
+  bullets can be separated by an empty line if they contain short paragraphs.
+
+- Syntax highlighting in fenced code blocks should use the `usage` `dvc`, and
+  `yaml` custom languages. `usage` is employed to show `dvc help` commands
   output in each command reference doc. `dvc` can be used to show
   [DVC-file](/doc/user-guide/dvc-file-format) contents, or examples of terminal
   commands and their output.
 
-> Check out any of the command reference `.md` source code to get a better idea.
+> Check out any of the command reference `.md` source code to get a better idea,
+> for example
+> [this very doc](https://github.com/iterative/dvc.org/blob/master/static/docs/user-guide/contributing-documentation.md).

static/docs/user-guide/contributing.md

@@ -265,7 +265,7 @@ $ ./scripts/ci/remove_hadoop.sh
 
 </details>
 
-## Code style guidelines
+## Code style guidelines (for Python)
 
 We are using [PEP8](https://www.python.org/dev/peps/pep-0008/?) and checking
 that our code is formatted with [black](https://github.com/ambv/black).
@@ -274,7 +274,7 @@ For [docstrings](https://www.python.org/dev/peps/pep-0257/#what-is-a-docstring),
 we try to adhere by the
 [Google Python Style Guide](https://github.com/google/styleguide/blob/gh-pages/pyguide.md#38-comments-and-docstrings).
 
-## Commit style guidelines
+## Commit message format guidelines
 
 Format: