Update documentation on deprecating and disabling formulae
Update documentation on deprecating and disabling formulae

This is based on the discussion at Homebrew/homebrew-core#91368.

A few reasons why we don't want to deprecate formulae that have
dependents:

1. This results in displaying warning messages to (at least some) users
   that they can't do anything about.
2. `test-bot` does not test deprecated formulae, so we risk breaking
   dependent formulae when one of its dependencies is not tested.
3. It is much harder to commit to a disable date for formulae with
   dependents because we don't know when we'll be able to wean
   dependents off of a deprecated formula.

I think it's important to have a disable date in mind when we deprecate
formulae. Otherwise, we might end up leaving formulae deprecated
indefinitely. This is bad because it teaches users to not take
deprecation warnings seriously.

JCount/brew,Homebrew/brew,MikeMcQuaid/brew,Homebrew/brew,JCount/brew,Homebrew/brew,MikeMcQuaid/brew,nandub/brew,MikeMcQuaid/brew,MikeMcQuaid/brew,nandub/brew,JCount/brew,nandub/brew,nandub/brew,Homebrew/brew,JCount/brew