bandwhich: add meta.changelog

bandwhich has two different changelogs:
1. the in-tree CHANGELOG.md
2. git tags/GitHub Releases

Unfortunately, the CHANGELOG.md contains fewer information from time to
time. One example would be
https://github.com/imsnif/bandwhich/blob/v0.22.0/CHANGELOG.md vs
https://github.com/imsnif/bandwhich/releases/tag/v0.22.0

In this case, the GitHub Release contains a lot more noise due to
various chore(deps) entries.

This is due to
b5e48ba9bb/.github/workflows/require-changelog-for-PRs.yml (L10-L11)

I'd argue, the CHANGELOG.md should be preferred here, but in the end
this isn't my package and not my call.

pkgs/tools/networking/bandwhich/default.nix

@@ -52,6 +52,7 @@ rustPlatform.buildRustPackage rec {
       the background using reverse DNS on a best effort basis.
     '';
     homepage = "https://github.com/imsnif/bandwhich";
+    changelog = "https://github.com/imsnif/bandwhich/blob/${src.rev}/CHANGELOG.md";
     license = licenses.mit;
     maintainers = with maintainers; [ Br1ght0ne figsoda ];
     platforms = platforms.unix;