add hotfix help

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)

hack/RELEASE-CHECKLIST.md

@@ -32,8 +32,21 @@ git fetch origin
 git branch -D release || true
 git checkout --track origin/release
 git checkout -b bump_$VERSION
+```
+
+If it's a regular release, we usually merge master
+```bash
 git merge origin/master
 ```
+Otherwise, if it is a hotfix release, we cherry-pick only the commits we want
+```bash
+#get the commits ids we want to cherry-pick
+git log
+#cherry-pick the commits starting from the oldest one, without including merge commits
+git cherry-pick <commit-id>
+git cherry-pick <commit-id>
+...
+```
 
 ### 2. Update CHANGELOG.md