Document release process

Author: jasonkarns

.github/CONTRIBUTING.md

@@ -0,0 +1,8 @@
+# Contributing
+
+## Releasing
+
+From a clean working copy, run `npm version major|minor|patch|VERSION`.
+This will bump the package version, commit, tag, and push.
+The tag-push event triggers the release workflow on GitHub.
+The workflow creates a GitHub Release from the tag and publishes to npm.