Fix the link to MultiDict in client_quickstart.rst (#5517)

(cherry picked from commit 13fd83e)

Author: webknjaz

docs/client_quickstart.rst

@@ -96,9 +96,9 @@ following code::
 
 You can see that the URL has been correctly encoded by printing the URL.
 
-For sending data with multiple values for the same key :class:`MultiDict` may be
-used; the library support nested lists (``{'key': ['value1', 'value2']}``)
-alternative as well.
+For sending data with multiple values for the same key
+:class:`~multidict.MultiDict` may be used; the library support nested lists
+(``{'key': ['value1', 'value2']}``) alternative as well.
 
 It is also possible to pass a list of 2 item tuples as parameters, in
 that case you can specify multiple values for each key::