feat(third_party/bazel): Check in rules_haskell from Tweag

third_party/bazel/rules_haskell/CONTRIBUTING.md

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+# Contributing to Bazel
+
+## Contributor License Agreement
+
+Contributions to this project must be accompanied by a Contributor License
+Agreement. You (or your employer) retain the copyright to your contribution,
+this simply gives us permission to use and redistribute your contributions as
+part of the project. Head over to <https://cla.developers.google.com/> to see
+your current agreements on file or to sign a new one.
+
+You generally only need to submit a CLA once, so if you've already submitted one
+(even if it was for a different project), you probably don't need to do it
+again.
+
+## Contribution process
+
+1. Explain your idea and discuss your plan with members of the team.
+   The best way to do this is to create an [issue][issue-tracker] or
+   comment on an existing issue.
+1. Prepare a git commit with your change. Don't forget to
+   add [tests][tests]. Run the existing tests with `bazel test //...`.
+   Update [README.md](./README.md) if appropriate.
+1. [Create a pull request](https://help.github.com/articles/creating-a-pull-request/).
+   This will start the code review process. **All submissions,
+   including submissions by project members, require review.**
+1. You may be asked to make some changes. You'll also need to sign the
+   CLA at this point, if you haven't done so already. Our continuous
+   integration bots will test your change automatically on supported
+   platforms. Once everything looks good, your change will be merged.
+
+[issue-tracker]: https://github.com/tweag/rules_haskell/issues
+[tests]: https://github.com/tweag/rules_haskell/tree/master/tests
+
+## Setting up your development environment
+
+Read how to [set up your development environment](https://bazel.build/contributing.html)