Document that `cabal.project` is used only for `packages`

I appreciate haskell-flake's support for cabal.project. I think it might be ignoring source-repository-package: https://cabal.readthedocs.io/en/stable/cabal-project.html#specifying-packages-from-remote-version-control-locations

haskell-multi-nix with example:
https://github.com/peterbecich/haskell-multi-nix/tree/source-repository-package-example

https://github.com/peterbecich/haskell-multi-nix/blob/source-repository-package-example/cabal.project

This should attempt to pull haskell/text bogus commit 123
cabal.project

packages:
    ./foo
    ./bar

source-repository-package
  type: git
  location: https://github.com/haskell/text.git
  tag: 123
  -- tag: 73620de89d43ee50de2d15b7bc0843bf6d6e9b9a

cabal build all fails as it should. However, nix build succeeds; I think it is getting text from NixPkgs as usual.

Cabal pulls the real commit 73620de correctly. nix build doesn't indicate if it is pulling this commit or not.

I know the text dependency could be specified in flake.nix: https://community.flake.parts/haskell-flake/dependency/#path

Thank you

Start with the linked cabal.project example and the Cabal documentation for source-repository-package, then reproduce the differing cabal build and nix build results. Confirm whether haskell-flake uses cabal.project only for packages, and document the observed limitation and expected behavior.