Add comment for messages on 'mediawiki.action.edit.editWarning'

In I43bf828654d342893a19656ddd4151c2558d2f63 the comment was added for
another usage.

Change-Id: I0510d069c6bc266d8d9e9a144daed2fc8dd7ebb9
Merge "Add comment for messages on 'mediawiki.action.edit.editWarning'"