Add brief contribution guide

CONTRIBUTING.md

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+This project is made possible by contributors like YOU! While all contributions are welcomed, please be sure and follow the following suggestions to help your PR get merged.
+
+## License
+
+This project uses an [Apache license](LICENSE). Be sure you're comfortable with the implications of that before working up a patch.
+
+## Review and merge process
+
+Review and merge duties are managed by [@kelseyhightower](https://github.com/kelseyhightower). Expect some burden of proof for demonstrating the marginal value of adding new content to the tutorial.
+
+Here are some examples of the review and justification process:
+- [#208](https://github.com/kelseyhightower/kubernetes-the-hard-way/pull/208)
+- [#282](https://github.com/kelseyhightower/kubernetes-the-hard-way/pull/282)
+
+## Notes on minutiae
+
+If you find a bug that breaks the guide, please do submit it. If you are considering  a minor copy edit for tone, grammar, or simple inconsistent whitespace, consider the tradeoff between maintainer time and community benefit before investing too much of your time.
+