Add explanation on translation jobs and scripts
Add explanation on translation jobs and scripts

The explanation on translation jobs and related scripts
is helpful for better understanding of monitoring translation
jobs status. The content was partly incorporated from
https://wiki.openstack.org/wiki/Translations/Infrastructure.

Change-Id: I10dbd98e5aaac2ecfc28eab8d292e5ade726d38c

openstack/i18n,openstack/i18n