ci: add create release action to ease releasing

.github/tag-release.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+export VERSION="${1:-}"
+
+echo "$VERSION" | grep -qEo '[0-9]+\.[0-9]+\.[0-9]+'
+if [ $? -ne 0 ]; then
+    echo "Invalid version number. Please use the format '0.2.0'"
+    exit 1
+fi
+
+# Bump version in pyproject.toml and sync the uv.lock file
+sed -i 's/^\(version = \).*$/\1'\"$VERSION\"'/' pyproject.toml
+uv sync
+
+git add pyproject.toml uv.lock
+git commit -m "chore: bump version to $VERSION"
+git tag -a "$VERSION" -m "$VERSION"
+
+git push origin main "$VERSION"

README.md

@@ -119,3 +119,12 @@ ruff check --fix
 # Format the code
 ruff format
 ```
+
+## Releasing
+
+Once all the changes have been merged into `main` for a release, use the
+[`.github/tag-release`](./.github/tag-release.sh) script to create a version bump commit in the
+right format, create, **and push** the tag ready for release.
+
+This could be automated with Github Actions - but commit signing gets a little complicated, so for
+now it's just a script that can be run by maintainers.