Merge pull request #1361 from horriblename/md-modeline-tw

doc: add textwidth modeline in release-note

Author: NotAShelf

docs/manual/release-notes/rl-0.9.md

@@ -150,3 +150,5 @@
 
 - Added [Selenen](https://github.com/kampfkarren/selene) for more diagnostics in
   `languages.lua`.
+
+<!-- vim: set textwidth=80: -->