Add changelog entry for ocaml#1187

Author: panglesd

CHANGES.md

@@ -26,6 +26,7 @@
   (@panglesd, #1076).
 - Added a `compile-asset` command (@EmileTrotignon, @panglesd, #1170)
 - Allow referencing assets (@panglesd, #1171)
+- Add a frontmatter syntax for mld pages (@panglesd, #1187)
 
 ### Changed