hal.cabal: Add CHANGELOG.md to extra-source-files

[endgame]

This'll make it show up as a change log on future hackage releases.

[IamfromSpace]

Didn't realize this wasn't included before! The cabal file is currently autogenerated, so we'll need to both add this to the package.yaml and update the cabal file hash. Been doing this a lot, so I added a patch-1 branch to this repo with a commit on top that does this; you can just pull it in to do so!

[endgame]

I think cabal check warns about such things, but not sure if it catches this one. Dunno about stack workflows.

[endgame]

Running hpack doesn't seem to add any more changes to the cabal file, so I think we're good to go.

[IamfromSpace]

Dunno about stack workflows.

Yeah, I'm still not sure the best way to handle this either, I've got an open issue #75. Without it's a pain for anyone who wants to pull the package from git using cabal, but it's a gotcha with it. 🤷‍♂️

Looks good to go here though!