Staged publishing support

publish/README.md

@@ -1,3 +1,24 @@
 # changesets/action/publish
 
-TODO
+Publishes packages with Changesets.
+
+Set the optional `stage` input to `true` or `false` to override
+`stagedPublishing` from the Changesets config. The input is tri-state: omitting
+it leaves the config in control. An explicit `stage` cannot be combined with a
+custom `script`; configure the script itself instead.
+
+When packages are staged, the action uploads a 30-day handoff and returns its
+exact id as `staged-release-artifact-id`. It also prints a topologically
+ordered approval command:
+
+```sh
+changeset stage approve <id...>
+```
+
+That command is only a convenience and uses the default registry. For custom
+or multiple registries, split the IDs into correctly scoped commands and pass
+`--registry` to each.
+
+After approval, pass the artifact id to
+`changesets/action/github-release` to verify publication and create Git tags
+and GitHub Releases.