[notification] fix documentation The doc say precommit, the code says postcommit. The code is right. We also clarify the documentation of another related operation looking suspiciously wrong but actually correct.

# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s specific hooks and operations"""