Fixed #17026 -- Improved wording of contrib.messages' storage backends section

docs/ref/contrib/messages.txt

@@ -54,7 +54,8 @@ Storage backends
 ----------------
 
 The messages framework can use different backends to store temporary messages.
-To change which backend is being used, add a `MESSAGE_STORAGE`_ to your
+If the default FallbackStorage isn't suitable to your needs, you can change
+which backend is being used by adding a `MESSAGE_STORAGE`_ to your
 settings, referencing the module and class of the storage class. For
 example::
 
@@ -62,7 +63,7 @@ example::
 
 The value should be the full path of the desired storage class.
 
-Four storage classes are included:
+Three storage classes are available:
 
 ``'django.contrib.messages.storage.session.SessionStorage'``
     This class stores all messages inside of the request's session. It
@@ -74,6 +75,8 @@ Four storage classes are included:
     messages are dropped if the cookie data size would exceed 4096 bytes.
 
 ``'django.contrib.messages.storage.fallback.FallbackStorage'``
+    This is the default storage class.
+
     This class first uses CookieStorage for all messages, falling back to using
     SessionStorage for the messages that could not fit in a single cookie.