Add release documentation

Signed-off-by: tdruez <[email protected]>

Author: tdruez

RELEASE.md

@@ -0,0 +1,31 @@
+# Release instructions for `ScanCode.io`
+
+### Automated release workflow
+
+- Create a new `release-x.x.x` branch
+- Update the version in:
+  - `setup.cfg` (2 entries)
+  - `scancodeio/__init__.py`
+  - `CHANGELOG.rst` (set date)
+- Commit and push this branch
+- Create a PR and merge once approved
+- Tag and push that tag. This will triggers the `pypi-release.yml` GitHub workflow that 
+  takes care of building the dist release files and upload those to pypi:
+  ```
+  VERSION=vx.x.x  # <- Set the new version here
+  git tag -a $VERSION -m ""
+  git push origin $VERSION
+  ```
+- Review the GitHub release created by the workflow at 
+  https://github.com/aboutcode-org/scancode.io/releases
+
+### Manual build
+
+```
+cd scancode.io
+source .venv/bin/activate
+pip install build
+python -m build --sdist --wheel --outdir dist/ .
+```
+
+The distribution files will be available in the local `dist/` directory.