add steps to prevent and allow main merge during the release procedure

Signed-off-by: Shinya Hayashi <[email protected]>

RELEASE.md

@@ -39,13 +39,14 @@ The result should look something like:
 Bump version
 ------------
 
-1. Determine a new version number by [checking the differences](https://github.com/topolvm/pie/compare/vX.Y.Z...main) since the last release. Then, define the `VERSION` variable.
+1. Go to [the "prevent main merge" rule setting page](https://github.com/topolvm/pie/settings/rules/1550843) and change the value of "Enforcement status" to `Active`.
+2. Determine a new version number by [checking the differences](https://github.com/topolvm/pie/compare/vX.Y.Z...main) since the last release. Then, define the `VERSION` variable.
 
     ```console
     VERSION=1.2.3
     ```
 
-2. Add a new tag and push it.
+3. Add a new tag and push it.
 
     ```console
     git switch main
@@ -54,15 +55,15 @@ Bump version
     git push origin v$VERSION
     ```
 
-3. Once a new tag is pushed, [GitHub Actions][] automatically
+4. Once a new tag is pushed, [GitHub Actions][] automatically
    creates a draft release note for the tagged version,
    builds a tar archive for the new release,
    and attaches it to the release note.
    
    Visit https://github.com/topolvm/pie/releases to check
    the result. 
 
-4. Edit the auto-generated release note
+5. Edit the auto-generated release note
    and remove PRs which contain changes only to the helm chart.
    Then, publish it.
 
@@ -79,6 +80,7 @@ You must change the version of Chart.yaml when making changes to the Helm Chart.
    https://github.com/topolvm/pie/actions/workflows/create-chart-update-pr.yaml
 
 2. Review and merge the auto-created PR.
+   - Before the merge, go to [the "prevent main merge" rule setting page](https://github.com/topolvm/pie/settings/rules/1550843) and change the value of "Enforcement status" to `Disabled`. 
 
 3. Manually run the GitHub Actions workflow for the release.