docs: add commands to prepare

Author: kenjis

admin/RELEASE.md

@@ -38,6 +38,8 @@ the changelog.
 
 * [ ] Clone **codeigniter4/shield** and resolve any necessary PRs
     ```console
+    rm -rf shield.bk
+    mv shield shield.bk
     git clone [email protected]:codeigniter4/shield.git
     ```
 * [ ] Merge any Security Advisory PRs in private forks