feat(pipelines): add post pipeline

Bug: misc:68
Change-Id: I37b1e702f722767ec5d1360e61a6a27b3800ccf1
diff --git a/zuul.d/pipelines.yaml b/zuul.d/pipelines.yaml
index 759f90f..6bea8cd 100644
--- a/zuul.d/pipelines.yaml
+++ b/zuul.d/pipelines.yaml
@@ -72,3 +72,17 @@
     failure:
       smtp:
         subject: 'gerrit @nightly-build failed'
+
+- pipeline:
+    name: post
+    description: |
+      Updates to a branch enter this pipeline.
+    manager: supercedent
+    precedence: low
+    post-review: True
+    trigger:
+      gerrit:
+        - event: ref-updated
+    failure:
+      smtp:
+        subject: "gerrit @post failed"