roll-dep: Add command used to make the roll in the CL description.

That's marketing 101. :)

R=sergeyberezin@chromium.org
BUG=

Change-Id: Ibbc1cd18650b7b601c27662fcb40ea7b15b40fc7
Reviewed-on: https://chromium-review.googlesource.com/439006Reviewed-by: Sergey Berezin <sergeyberezin@chromium.org>
Commit-Queue: Sergey Berezin <sergeyberezin@chromium.org>

roll_dep.py

@@ -144,7 +144,7 @@ def roll(root, deps_dir, roll_to, key, reviewers, bug, no_log, log_limit,
       # Keep the first N log entries.
       logs = ''.join(logs.splitlines(True)[:log_limit]) + '(...)\n'
     log_section += logs
-  log_section += '\n'
+  log_section += '\n\nCreated with:\n  roll-dep %s\n' % deps_dir
 
   reviewer = 'R=%s\n' % ','.join(reviewers) if reviewers else ''
   bug = 'BUG=%s\n' % bug if bug else ''