quickstart.rst: r.json() can raise JSONDecodeError on Py3

% `python2 -c "import requests ; requests.get('https://github.com').json()"`
% `python3 -c "import requests ; requests.get('https://github.com').json()"`

docs/user/quickstart.rst

@@ -150,7 +150,9 @@ There's also a builtin JSON decoder, in case you're dealing with JSON data::
 
 In case the JSON decoding fails, ``r.json()`` raises an exception. For example, if
 the response gets a 204 (No Content), or if the response contains invalid JSON,
-attempting ``r.json()`` raises ``ValueError: No JSON object could be decoded``.
+attempting ``r.json()`` raises ``ValueError: No JSON object could be decoded`` on
+Python 2 and raises ``simplejson.JSONDecodeError`` or ``json.JSONDecodeError`` on
+Python 3.
 
 It should be noted that the success of the call to ``r.json()`` does **not**
 indicate the success of the response. Some servers may return a JSON object in a