Add release note for security group set refactor

Add a release note for [1].

[1] https://review.openstack.org/#/c/287763/

Change-Id: I30812c3ead477267dc7e3dc774c09b3435152eb9
Partial-Bug: #1519511
Implements: blueprint neutron-client

Author: rtheis

releasenotes/notes/bug-1519511-74bab0e0d32db043.yaml

@@ -1,7 +1,10 @@
 ---
 fixes:
-  - |
-    Ignore the ``security group list`` command ``--all-projects`` option
+  - Ignore the ``security group list`` command ``--all-projects`` option
     for Network v2 since security groups will be displayed for all projects
     by default (admin only).
     [Bug `1519511 <https://bugs.launchpad.net/bugs/1519511>`_]
+  - The ``security group set`` command now uses Network v2 when
+    enabled which allows the security group name and description
+    to be set to an empty value.
+    [Bug `1519511 <https://bugs.launchpad.net/bugs/1519511>`_]