Add info on <pre> tags to markdown reference and style guide (#35111)

Co-authored-by: Sarah Schneider <sarahs@users.noreply.github.com>

contributing/content-style-guide.md

@@ -49,6 +49,7 @@ Within code blocks:
 - Do not use markup before the command output.
 - Only use `$` before the command itself if you’re showing the command’s output in the same block.
 - If your code example includes `{` or `}` that should render, wrap that section in `{% raw %}` `{% endraw %}` to disable Liquid processing for that section.
+- If your code example includes content that should be parsed (for example, HTML tags to format text), wrap that section in `<pre>` `</pre>` tags to parse rather than escape the content in the section.
   - **Use**:
 
     ```