Fix missing rule description in HACKING.rst
Fix missing rule description in HACKING.rst

The description of N363 hacking rule is missing
in HACKING.rst.
Add the description.

Change-Id: I036a48612fcd256df4ccbd2ebba814bf3ed7a1c2
Closes-Bug: #1840862

mahak/nova,mahak/nova,openstack/nova,openstack/nova,rahulunair/nova,klmitch/nova,klmitch/nova,klmitch/nova,mahak/nova,rahulunair/nova,openstack/nova,rahulunair/nova,klmitch/nova