docs: Add very simple guide on creating releases (#26)

Author: sbernauer

CONTRIBUTING.md

@@ -0,0 +1,6 @@
+### How to create a release
+
+Open a PR to bump the `project.version` in `authorizer/pom.xml`, you can title the PR something like `chore: Release x.x.x`.
+
+The Git tag as well as the GitHub release is automatically created by CI after merge.
+Don't create them yourself, as the CI will attach a pre-build NAR file.