document the release workflow and associated tooling

CONTRIBUTING.md

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+## release workflow
+
+We use a combination of [GitHub Actions](https://docs.github.com/en/actions) and [goreleaser](https://goreleaser.com/)
+
+Configurations for those shouldn't generally require adjusting, but if they do, they are found underneath `.github` and `.goreleaser.yml`
+
+In order to release:
+
+1) Merge your changes to master
+2) Push a tag following semVer. If you are unsure of what version to assign, you can find the concepts described here: https://semver.org/
+3) Verify the github action defined in .github/ completed and a new release is available. You can see the status in the github web UI.
+