add codeowners and a contributing.md (#2)

* add codeowners and a contributing.md

* add release workflow
maybe we can automate this in the future

* add token things to todo

CODEOWNERS

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+* @pantheon-systems/site-experience @pantheon-systems/devrel

CONTRIBUTING.md

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+# Contributing
+
+The default development branch is `develop`. [Autotag](https://github.com/pantheon-systems/autotag) automatically tags a release on merges to `main`.
+
+This repository is mostly owned and maintained by [Chris Reynolds](https://github.com/jazzsequence) ([DevRel](https://github.com/orgs/pantheon-systems/teams/devrel)) and is intended _exclusively_ for internal Pantheon projects. (It is a public repository by necessity, because it interacts with other public repositories.)
+
+Direct commits to `develop` are discouraged. Squash merges are generally preferred.
+
+## Releases
+
+When `develop` is ready for a release, merge `develop` into `main` and push to main.
+
+```bash
+git checkout develop && git pull
+git checkout main && git pull
+git merge develop --ff-only
+git push origin main
+```
+
+## Todo
+
+- [ ] Break out bash scripts into separate files rather than everything being inside the `action.yml`.
+- [ ] Automate releases.
+- [ ] Figure out a generic Pantheon token that can be used universally for this action across repositories that's not tied to an individual user.