DOC Document how to include filenames for code blocks

en/05_Contributing/02_Documentation.md

@@ -111,6 +111,8 @@ documenting, there shouldn't be any "frequently asked questions" left.
 - Use an empty line to separate paragraphs.
 - Sentence case your bullet points. If a bullet point is a full sentence then end with a full stop. If it is a sentence fragment or a comma separated list, full stops are not required.
 - All code blocks must have an appropriate syntax highlighting hint. For plain text, use "text".
+- If it's useful to include the filename that a code block relates to, do so in a comment in the first line of the code block.
+  - Don't place a blank line after this comment, unless the next line is also a comment.
 - Code examples should follow our [coding conventions](./coding_conventions).
 - Use `App` when the code requires a vendor name (e.g. as the root for namespaces).
 - Do not put a `$` in front of lines of bash code examples.