Diviner: Improve documentation for remarkup code blocks
Summary:
Improve remarkup reference documentation.
- Added a heading for Code Blocks
- Added a sentence mentioning the ```lang syntax which was added in {T15481}
Test Plan:
- Run bin/diviner generate to regen diviner docs.
- Check out the code blocks section of Remarkup Reference
Reviewers: valerio.bozzolan, O1 Blessed Committers
Reviewed By: valerio.bozzolan, O1 Blessed Committers
Subscribers: tobiaswiese, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D25547