Print message when waiting for editor

Running "git cl upload" can take a while so I tend to switch to other
tasks while it runs. On a regular basis I get frustrated because it is
taking an extremely long time only to realize that it has been waiting
for me.

This change adds a message saying "Waiting for editor..." to make it
clear who is waiting for whom.

Change-Id: I8cf08c3d2be0c7a843a4c07529682bc049b30426
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2503689
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>

git_cl.py

@@ -2659,6 +2659,7 @@ class ChangeDescription(object):
     if not any((has_issue(line) for line in self._description_lines)):
       self.append_footer('Bug: %s' % prefix)
 
+    print('Waiting for editor...')
     content = gclient_utils.RunEditor(self.description, True,
                                       git_editor=settings.GetGitEditor())
     if not content: