Add instructions to handle failed releases. (istio#870)

* polish

* add word

* polish

* polish


Former-commit-id: 78b66f5

release/README.md

@@ -65,25 +65,44 @@ $ alias githubctl="${PWD}/bazel-bin/toolbox/githubctl/githubctl"
 
 The release process goes like the following:
 
+Step 1: Tag the release.
 ```
-# Tag the release
 $ githubctl --token_file=<github token file> \
     --op=tagIstioDepsForRelease \
     --base_branch=<release branch or master>
+```
+
+Step 2: The previous command triggers rebuild and retagging on pilot, proxy, mixer and auth. 
+ Wait for them to finish. Check build job status [here](https://console.cloud.google.com/gcr/builds?project=istio-io&organizationId=433637338589)
 
-# The previous command triggers rebuild and retagging on pilot, mixer and auth.
-# Wait for them to finish, then create an update PR in istio/istio
+Step 3: Create an update PR in istio/istio.
+```
 $ githubctl --token_file=<github token file> \
-    --op=updateIstioVersion --base_branch=<release branch or master>
+    --op=updateIstioVersion --base_branch=<release branch or master> 
+```
+
+Step 4: Request PR approval and wait for the PR to be merged.
 
-# Wait for the PR to be merged.
-# Then create the release in GitHub, upload the artifacts,
-# advance next release tag, update download script with latest release:
+Step 5: Finalize the release. This creates the release in GitHub, uploads the artifacts,
+ advances next release tag, and updates download script with latest release:
+```
 $ githubctl --token_file=<github token file> \
     --op=uploadArtifacts --base_branch=<release branch or master> \
     --next_release=0.2.2
 ```
 
+```<github token file>``` is a text file containing the github peronal access token setup following the [instruction](https://github.com/istio/istio/blob/master/devel/README.md#setting-up-a-personal-access-token)
+
+### Revert a failed release
+
+When a release failed, we need to clean up partial state before retry. A common case is that a build failed when doing Step 2 from the above. We need to rollback the Step 1 by doing the following: 
+
+1. Remove new tags on the repos by finding the release and click "delete tag".
+   * https://github.com/istio/auth/releases
+   * https://github.com/istio/mixer/releases
+   * https://github.com/istio/pilot/releases
+1. Proceed with the above release process step [1-5].
+
 ## Manual release process (DEPRECATED)
 
 ### Creating tags