Mark your calendars! Friday, May 12th has been designated MediaWiki Documentation Day. This is a day to put aside normal development work and focus on improving MediaWiki documentation. This includes documentation for users, wiki administrators, and developers.
Anyone with a good understanding of any particular area of MediaWiki software (broadly construed to include gadgets, bots, libraries, API frameworks, etc.) is encouraged to add or update on-wiki documentation, in-code documentation, READMEs, etc. And even if you don't feel like you know enough to improve the documentation, you can also participate by flagging out-dated documentation or creating documentation requests on the wiki page.
Coordination for Documentation Day is happening at: * https://www.mediawiki.org/wiki/MediaWiki_Documentation_Day_2017 * https://phabricator.wikimedia.org/T126500
For more details, please refer to the wiki page above. This is a completely ad hoc event, so feel free to adapt it, evolve it, expand it, hijack it, promote it, or ignore it. Cheers!