docs(release): stop merges during a release and add the Marketplace step (#132)

A merge to main after the release commit stops the plan job. The
procedure now tells the owner to stop other merges first. The new last
section publishes the action to the GitHub Marketplace.

Signed-off-by: Bart Waardenburg <bart@waardenburg.dev>

Author: BartWaardenburg

docs/release-procedure.md

@@ -84,6 +84,11 @@ commit collects the fragments.
 
 ## Prepare the release commit
 
+From the merge of the release pull request until the tag push, `main` must
+not change. The `plan` job and `scripts/publish-github-release.mjs` stop when
+`origin/main` is not the release commit. Before step 1, stop each other
+session and pull request that can merge to `main`, also auto-merge.
+
 1. Make a branch from the newest `main`: `git switch -c chore/release-vX.Y.Z`.
 2. Run `node scripts/changelog-fragments.mjs collect`. The command moves each
    fragment into `[Unreleased]` and deletes the fragment files.
@@ -195,6 +200,19 @@ release creation fails after the tag push, keep the signed tag. Remove only an
 incomplete draft, then run `gh release create` again with the same values.
 Never move or create the signed tag again.
 
+## Publish the action to the GitHub Marketplace
+
+The GitHub Marketplace reads `action.yml` at the release tag. Do this step
+after the release creation:
+
+1. Open the release on GitHub and click **Edit**.
+2. Select **Publish this Action to the GitHub Marketplace**.
+3. Select a primary category, for example **Code quality**.
+4. Click **Update release**.
+
+The Marketplace rejects a `description` of 125 characters or more.
+`action/tests/run.sh` fails before a release when the description is too long.
+
 ## Change the release environment after this procedure merges
 
 The `release` environment admitted only the tag rule `v*` for the 0.1.0