docs: add RELEASING.md (#146)

Signed-off-by: Niels Pardon <par@zurich.ibm.com>
Co-authored-by: Ben Bellick <36523439+benbellick@users.noreply.github.com>

Author: nielspardon

RELEASING.md

@@ -0,0 +1,14 @@
+# Releasing substrait-python
+
+Given that you are a Substrait committer or PMC member and have the appropriate permissions, releasing a new version of substrait-python is done by simply creating new Github Release through the UI:
+
+1. Go to https://github.com/substrait-io/substrait-python/releases
+2. Click `Draft a new release`
+3. Enter the version to be released in the `Tag` field prefixed with a lower case `v`, e.g. `v0.99.0`. Then click `Create new tag` which tells Github to create the tag on publication of the release.
+4. Click `Generate release notes` which will automatically populate the release title and release notes fields.
+5. If you are happy with the release notes and you are ready for an immediate release simply click `Publish release` otherwise save the release as a draft for later.
+6. Monitor the Github Actions release build for the newly created release and tag.
+
+## Versioning
+
+substrait-python follows semantic versioning as described for the Substrait specification here: https://substrait.io/spec/versioning/.