update release documentation (#56)

Signed-off-by: Brian DeHamer <bdehamer@github.com>

RELEASE.md

@@ -11,6 +11,14 @@ Follow the steps below to tag a new release for the `actions/attest` action.
    gh release create vX.X.X
    ```
 
+1. Move (or create) the major version tag to point to the same commit tagged
+   above:
+
+   ```shell
+   git tag -fa vX -m "vX"
+   git push origin vX --force
+   ```
+
 1. As appropriate, update any actions like
    [`actions/attest-build-provenance`](https://github.com/actions/attest-build-provenance)
    and [`actions/attest-sbom`](https://github.com/actions/attest-sbom) which