Update Flutter-Cherrypick-Process.md

Update manual CP process to include step about `cp: review` label
diff --git a/docs/releases/Flutter-Cherrypick-Process.md b/docs/releases/Flutter-Cherrypick-Process.md
index 1abd8e0..63fcc27 100644
--- a/docs/releases/Flutter-Cherrypick-Process.md
+++ b/docs/releases/Flutter-Cherrypick-Process.md
@@ -29,7 +29,8 @@
   - Risk (What is the risk level of this cherry-pick?)
   - Test Coverage (Are you confident that your fix is well-tested by automated tests?)
   - Validation Steps (What are the steps to validate that this fix works?)
-4. [STABLE ONLY] Ensure that your cherry-pick PR updates CHANGELOG.md.
+4. Add the label `cp: review` to your PR
+5. [STABLE ONLY] Ensure that your cherry-pick PR updates CHANGELOG.md.
 
 ## Frequently asked questions