Add releasing docs (#4)

RELEASING.md

@@ -0,0 +1,15 @@
+# Release Process
+
+1. Add and push a signed tag:
+
+   ```sh
+   TAG='v<version>'
+   COMMIT='<commit-sha>'
+   git tag -s -m $TAG $TAG $COMMIT
+   git push upstream $TAG
+   ```
+
+1. Create a GitHib Release named `v<version>` with `v<version>` tag.
+
+   The release description should include all the release notes
+   from the [`CHANGELOG.md`](CHANGELOG.md) for this release.