Fix doc on keystoneauth session api usage

This fixes documentation on client creation with keystoneauth
session api.

Change-Id: I0f6bb6f4f9bbaa84b5185c0a9e9db6a4184702d4
Partial-Bug: #1646539

doc/source/index.rst

@@ -22,18 +22,23 @@ Once you have done so, you can use the API like so::
 
 Alternatively, you can create a client instance using the keystoneauth session API::
 
+  >>> from keystoneauth1 import loading
   >>> from keystoneauth1 import session
-  >>> from keystoneauth1.identity import v3
   >>> from heatclient import client
-  >>> password = v3.PasswordMethod(username=USERNAME,
+  >>> loader = loading.get_plugin_loader('password')
+  >>> auth = loader.load_from_options(auth_url=AUTH_URL,
+  ...                                 username=USERNAME,
   ...                                 password=PASSWORD,
-  ...                              user_domain_name=DEFAULT)
-  >>> auth = v3.Auth(auth_url=AUTH_URL, auth_methods=[password],
   ...                                 project_id=PROJECT_ID)
   >>> sess = session.Session(auth=auth)
-  >>> heat = client.Client('1', endpoint=heat_url, session=sess)
+  >>> heat = client.Client('1', session=sess)
   >>> heat.stacks.list()
 
+If you have PROJECT_NAME instead of a PROJECT_ID, use the project_name
+parameter. Similarly, if your cloud uses keystone v3 and you have a DOMAIN_NAME
+or DOMAIN_ID, provide it as `user_domain_(name|id)` and if you are using a
+PROJECT_NAME also provide the domain information as `project_domain_(name|id)`.
+
 For more information on keystoneauth API, see `Using Sessions`_.
 
 .. _Using Sessions: http://docs.openstack.org/developer/keystoneauth/using-sessions.html