Fix domain name in install doc (2)

Commit 3f1a89c7dd changed most of the
install docs to use "Default" instead of "default" for project/user
domain names according to the keystone docs, but the install doc for
PyPI has been missed. This patch fixes it accordingly.

Change-Id: I2e92730ff5819bf49cf1b286356870fdb9c6ece5
Story: #2006652
Task: #36894
(cherry picked from commit 81da427b33)

doc/source/install/from-pypi.rst

@@ -160,8 +160,8 @@ configuration settings not mentioned here.
         auth_url = http://controller:5000/
         memcached_servers = controller:11211
         auth_type = password
-        project_domain_name = default
-        user_domain_name = default
+        project_domain_name = Default
+        user_domain_name = Default
         project_name = service
         username = placement
         password = PLACEMENT_PASS
@@ -169,6 +169,11 @@ configuration settings not mentioned here.
      Replace ``PLACEMENT_PASS`` with the password you chose for the
      ``placement`` user in the Identity service.
 
+     .. note::
+
+        The value of ``user_name``, ``password``, ``project_domain_name`` and
+        ``user_domain_name`` need to be in sync with your keystone config.
+
    * You may wish to set the :oslo.config:option:`debug` option to ``True`` to
      produce more verbose log output.