add instructions how to release

HOW-TO-RELEASE.md

@@ -0,0 +1,25 @@
+# Release process
+
+How to create a new [release](../../releases).
+
+## Releasing
+
+The release process is automated thanks to:
+- https://github.com/djspiewak/sbt-github-actions#integration-with-sbt-ci-release
+- https://github.com/olafurpg/sbt-ci-release
+
+To release, push a git tag:
+
+```
+git tag -a v0.1.0 -m "v0.1.0"
+git push origin v0.1.0
+```
+Note that the tag version MUST start with `v`.
+
+Wait for the [CI pipeline](../../actions) to release the new version. Publishing the artifacts on maven central can take time.
+
+## Updating the release notes
+
+Open the [releases](../../releases). A draft should already be prepared.
+
+Edit the draft release to set the released version. Complete the release notes if necessary. And save it.