Add call for maintainers to the README

README.md

+> ⚠️ Oh My Fish has been unmaintained for years, and certain parts of it may not work for you. A few themes and packages are currently broken, and the code is due a significant overhaul. The current set of maintainers have ran out of steam, so if you are interested in becoming a maintainer send an email to *oh-my-fish [at] googlegroups.com*.
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