haskell: add link to Hydra build report for haskell-updates branch to PR message

maintainers/scripts/haskell/merge-and-open-pr.sh

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 This PR is the regular merge of the \`haskell-updates\` branch into \`master\`.
 
-This branch is being continually built and tested by hydra at https://hydra.nixos.org/jobset/nixpkgs/haskell-updates.
+This branch is being continually built and tested by hydra at https://hydra.nixos.org/jobset/nixpkgs/haskell-updates. You may be able to find an up-to-date Hydra build report at [cdepillabout/nix-haskell-updates-status](https://github.com/cdepillabout/nix-haskell-updates-status).
 
 We roughly aim to merge these \`haskell-updates\` PRs at least once every two weeks. See the @NixOS/haskell [team calendar](https://cloud.maralorn.de/apps/calendar/p/Mw5WLnzsP7fC4Zky) for who is currently in charge of this branch.