Helping out with the MediaWiki software means that Wikivoyage works better. It also shows that we're grateful for this great software, and that we want to give something back to the people who worked so hard to make it. It builds up goodwill, since anything we do for MediaWiki will help users for all the sites using MediaWiki.
Some things to do to help with MediaWiki:
Report bugs. MediaWiki has a bug tracker; you can use that tool to submit new bugs. Make sure that it's a problem with the software and not with Wikivoyage first, of course, and check to make sure that the bug you've identified isn't already in the tracker. But identifying bugs helps developers improve the quality of the software.
Suggest enhancements. If you have a good idea for how to enhance the MediaWiki software, submit a Request For Enhancement ("RFE") on the SourceForge site. Again, try to make sure that the request hasn't already been made in the tracker. Identifying new features for MediaWiki can make it easier for users of all MediaWiki sites to make great content.
Submit patches. If you know PHP, you can review the features and bugs that have been submitted, and try to create patches for them. Patches for MediaWiki should be submitted to the Wikimedia developers mailing list.
Write documentation. There's a Wiki-based, user-edited user's guide for MediaWiki on the Wikipedia meta-site. You can contribute to the user's guide, which will help all users of the software.
Join the MediaWiki project. If you know PHP, you can join the MediaWiki SourceForge project and help with the maintenance of the MediaWiki codebase and its further development.
