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

import json before using json module
(cherry picked from commit 1dbce04d0e3e93b715eb0d8024da396361759d16)
diff --git a/Doc/tutorial/inputoutput.rst b/Doc/tutorial/inputoutput.rst
index d354246..d6c3cb6 100644
--- a/Doc/tutorial/inputoutput.rst
+++ b/Doc/tutorial/inputoutput.rst
@@ -390,6 +390,7 @@
 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"]'