Add guidance for HTTP status codes and methods

Treat HTTP status codes like code, and wrap them in inline code
blocks.

doc/development/documentation/styleguide.md

@@ -1315,6 +1315,9 @@ the documentation site, but will be displayed on GitLab's `/help`.
   added to code blocks. To make things easier for the user, always add a full
   code block for things that can be useful to copy and paste, as they can easily
   do it with the button on code blocks.
+- HTTP methods (`HTTP POST`) and HTTP status codes, both full (`404 File Not Found`)
+  and abbreviated (`404`), should be wrapped in inline code blocks when used in sentences.
+  For example: Send a `DELETE` request to delete the runner. Send a `POST` request to create one.
 - Add a blank line above and below code blocks.
 - When providing a shell command and its output, prefix the shell command with `$`
   and leave a blank line between the command and the output.