Add haskell-debugger notes to contributing guide

[philderbeast]

What is wrong with the docs?
Please add to the CONTRIBUTING.md, a section on how to configure and use the haskell-debugger with cabal-install.

[ulysses4ever]

Is there any prior art for this?

[geekosaur]

I think there's something on Discourse? (https://discourse.haskell.org/t/the-haskell-debugger-for-ghc-9-14/13499)