Document -package-env correctly

For a few GHCs now, I'm used to seeing a note as GHCi launches that it has loaded my default package environment file, in ~/.ghc/arch-version/environments/default. Today, when working in GHC 9.2.1, I was surprised that some package wasn't available, and so I looked for this line and was surprised not to find it.

Yet the documentation still says that it loads this default.

I think the documentation should be updated, and a release note added.