[Release tools] Add instructions how to close the auto-roller.

R=machenbach@chromium.org
BUG=494641
LOG=N
NOTRY=true

Review URL: https://codereview.chromium.org/1217173003

Cr-Commit-Position: refs/heads/master@{#29404}

tools/release/chromium_roll.py

@@ -9,14 +9,15 @@ import sys
 
 from common_includes import *
 
-
 ROLL_SUMMARY = ("Summary of changes available at:\n"
                 "https://chromium.googlesource.com/v8/v8/+log/%s..%s")
 
-
 ISSUE_MSG = (
 """Please follow these instructions for assigning/CC'ing issues:
-https://code.google.com/p/v8-wiki/wiki/TriagingIssues""")
+https://code.google.com/p/v8-wiki/wiki/TriagingIssues
+
+Please close rolling in case of a roll revert:
+https://v8-roll.appspot.com/""")
 
 class Preparation(Step):
   MESSAGE = "Preparation."