bpo-30621: Update Input Output Tutorial Example(GH-2074) (GH-2120)

import json before using json module
(cherry picked from commit 1dbce04)

Author: Mariatta

Doc/tutorial/inputoutput.rst

@@ -390,6 +390,7 @@ sent over a network connection to some distant machine.
 If you have an object ``x``, you can view its JSON string representation with a
 simple line of code::
 
+   >>> import json
    >>> json.dumps([1, 'simple', 'list'])
    '[1, "simple", "list"]'