Conveying breaking changes

[frafra]

Something important for existing users relying on pre-commit git hook: they should pre-commit uninstall && prek install.
We should think about a good way to conveying this change to the users.

Originally posted by @frafra in #45

How to deal with breaking changes?

We will release a 0.3.0 version with prek instead of pre-commit, but how to handle this migration? It might happen again in the future.