Detailed help message for QoS max-burst-kbps value

For QoS rule type bandwidth-limit the max-burst-kbps value for ovs and
linuxbridge is suggested to be 80% of the maxkbps value, let's give a
detailed help message for the CLI user.
For details see https://docs.openstack.org/neutron/queens/admin/
config-qos.html#user-workflow

Change-Id: Ia6e38ec7052b7af64880c2f4c5e242d7cb980df5
Closes-Bug: #1777866

openstackclient/network/v2/network_qos_rule.py

@@ -141,7 +141,10 @@ def _add_rule_arguments(parser):
         dest='max_burst_kbits',
         metavar='<max-burst-kbits>',
         type=int,
-        help=_('Maximum burst in kilobits, 0 means automatic')
+        help=_('Maximum burst in kilobits, 0 or not specified means '
+               'automatic, which is 80%% of the bandwidth limit, which works '
+               'for typical TCP traffic. For details check the QoS user '
+               'workflow.')
     )
     parser.add_argument(
         '--dscp-mark',