Add documentation.

Change-Id: I8197ec2e52596fa4136f8af9aa93ea06e56d4d0d
diff --git a/etc/layout.yaml-sample b/etc/layout.yaml-sample
index 39e7aab..8edc794 100644
--- a/etc/layout.yaml-sample
+++ b/etc/layout.yaml-sample
@@ -2,7 +2,7 @@
   - name: check
     manager: IndependentQueueManager
     trigger:
-      - event: patchset-uploaded
+      - event: patchset-created
     success:
       verified: 1
     failure: