Updated mediawiki/extensions
Project: mediawiki/extensions/VisualEditor  9a31ff266f8e77b3761992ef87c7fa6d4bd325d3

Describe commit message guidelines in CONTRIBUTING.md

Add a brief note pointing to the gerrit commit message guidelines.

Change-Id: Ia5d9a167b9510d09831e4d90daa0179af07ed5d3