Consider archiving library to make it more obvious it is no longer supported

[mkobit]

https://docs.github.com/en/repositories/archiving-a-github-repository/archiving-repositories

Although the top of the README says This library is obsolete, it is easy to scroll past when looking for the general shape of the library to see if it is useful. One last minor tweak to the settings will make it a bit more immediate to uses who come across this repository that it is no longer supported with the differently colored header: