release: cargo-release config for tag-driven releases

`cargo release patch --execute` now does what the last three releases
did by hand: bump Cargo.toml/Cargo.lock, rewrite PKGBUILD's pkgver,
stamp the "## Unreleased" changelog section with version and date,
commit as "release X.Y.Z", tag vX.Y.Z and push commit and tag to the
gitea remote (not `origin`, which is the GitHub upstream). The tag then
triggers .gitea/workflows/release.yml as before. No crates.io publish.

CHANGELOG.md gets a standing "## Unreleased" section to collect entries
between releases; README documents the flow.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -79,6 +79,17 @@ The launcher also accepts prefix operators to change its mode:
 
 - Scaling of any kind - all sizes are currently hardcoded in pixels
 
+## Releasing
+
+Releases are cut with [cargo-release](https://github.com/crate-ci/cargo-release) (`cargo install cargo-release`), configured in `release.toml`. Put a line for each change under `## Unreleased` in `CHANGELOG.md` as you go, then on a clean `master`:
+
+```
+cargo release patch            # dry run: shows the bump, replacements and tag
+cargo release patch --execute  # do it (minor/major or an explicit version also work)
+```
+
+This bumps `Cargo.toml`, `Cargo.lock` and `PKGBUILD` to the same version, stamps the changelog section with the version and date, commits as `release X.Y.Z`, tags `vX.Y.Z` and pushes commit and tag to the `gitea` remote. The tag triggers `.gitea/workflows/release.yml`, which builds the package per architecture and uploads it to the `[uhhm]` registry. The workflow refuses a tag whose version disagrees with `PKGBUILD` or `Cargo.toml`, which cannot happen when the tag comes from cargo-release.
+
 ## How to discuss
 
 Go to #kennylevinsen @ irc.libera.chat to discuss, or use [~kennylevinsen/public-inbox@lists.sr.ht](https://lists.sr.ht/~kennylevinsen/public-inbox).