REALEASING.md: add documentation on how to cut releases (#122)

Author: xrmx

RELEASING.md

@@ -0,0 +1,21 @@
+### Releasing
+
+Releases tags are signed so you need to have a PGP key set up, you can follow Github documentation on [creating a key](https://docs.github.com/en/authentication/managing-commit-signature-verification/generating-a-new-gpg-key) and
+on [telling git about it](https://docs.github.com/en/authentication/managing-commit-signature-verification/telling-git-about-your-signing-key). Alternatively you can sign with a SSH key, remember you have to upload your key
+again even if you want to use the same key you are using for authorization.
+Then make sure you have SSO figured out for the key you are using to push to github, see [Github documentation](https://docs.github.com/articles/authenticating-to-a-github-organization-with-saml-single-sign-on/).
+
+If you have commit access, the process is as follows:
+
+1. Update the version in `ecs_logging/__init__.py` according to the scale of the change. (major, minor or patch)
+1. Update `CHANGELOG.md`.
+1. Commit changes with message `update CHANGELOG and rev to vX.Y.Z`
+ where `X.Y.Z` is the version in `ecs_logging/__init__.py`
+1. Open a PR against `main` with these changes leaving the body empty
+1. Once the PR is merged, fetch and checkout `upstream/main`
+1. Tag the commit with `git tag -s X.Y.Z`, for example `git tag -s 2.2.0`.
+ Copy the changelog for the release to the tag message, removing any leading `#`.
+1. Push tag upstream with `git push upstream --tags` (and optionally to your own fork as well)
+1. After tests pass, Github Actions will automatically build and push the new release to PyPI.
+1. Edit and publish the [draft Github release](https://github.com/elastic/ecs-logging-python/releases).
+ Substitute the generated changelog with one hand written into the body of the release.