Survey: Use cases for shards' `postinstall`

In the case of Anyolite, this isn’t really a postinstall issue but rather crystal-lang/crystal#9030 (which should be resolved by crystal-lang/crystal#13567) but this is definitely a justified reason to use postinstall, users would just need to ensure that other dependencies like Ruby and Rake are installed before installing (which one can assume so if you are using a library like Anyolite).