Document jira link creation and persistent content.

overview/contributing/jira_tickets.rst
--------------------------------------
  o Added a howto for attaching URLs to a jira ticket.
  o Note jenkins jobs disappear due to aging, suggest including a {gerrit,github} url as well.

[HOWTO: test]
% git clone ssh://gerrit.opencord.org:29418/voltha-docs.git
% cd voltha-docs
% git review -d I6582baab45ebafc37324cddd5afd5f8331e0c6d1

% make reload

% make lint
% make test

Change-Id: I6582baab45ebafc37324cddd5afd5f8331e0c6d1
2 files changed