Hi.
As https://bugzilla.wikimedia.org/show_bug.cgi?id=50552#c0 explains, MediaWiki's current README file isn't as strong as it could be. Following discussion on that bug report, there's now a wiki page that can be used to freely edit MediaWiki's README: https://www.mediawiki.org/wiki/README.
In the past few days, I think significant progress has been made in cleaning up the README. If anyone has thoughts about what it should or shouldn't include, please feel free to reply on this mailing list, on the bug report, or be bold and contribute directly to the wiki page. :-)
MZMcBride