[AIRFLOW-XXX] Add a doc on how to add a new role in RBAC UI (#4426)

docs/howto/add-new-role.rst

@@ -0,0 +1,33 @@
+..  Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
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+    to you under the Apache License, Version 2.0 (the
+    "License"); you may not use this file except in compliance
+    with the License.  You may obtain a copy of the License at
+
+..    http://www.apache.org/licenses/LICENSE-2.0
+
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+    software distributed under the License is distributed on an
+    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+    KIND, either express or implied.  See the License for the
+    specific language governing permissions and limitations
+    under the License.
+
+
+Add a new role in RBAC UI
+=========================
+
+There are five roles created for Airflow by default: Admin, User, Op, Viewer, and Public.
+The master branch adds beta support for DAG level access for RBAC UI. Each DAG comes with two permissions: read and write.
+
+The Admin could create a specific role which is only allowed to read / write certain DAGs. To configure a new role, go to ``Security`` tab
+and click ``List Roles`` in the new UI.
+
+.. image:: ../img/add-role.png
+.. image:: ../img/new-role.png
+
+
+The image shows a role which could only write to example_python_operator is created.
+And we could assign the given role to a new user using ``airflow users --role`` cli command.

docs/howto/index.rst

@@ -27,6 +27,7 @@ configuring an Airflow environment.
 .. toctree::
     :maxdepth: 2
 
+    add-new-role
     set-config
     initialize-database
     operator
@@ -39,3 +40,4 @@ configuring an Airflow environment.
     run-with-systemd
     run-with-upstart
     use-test-config
+