update docs

Signed-off-by: Kenneth Reitz <me@kennethreitz.org>

docs/index.rst

@@ -29,18 +29,23 @@ Tablib is an :ref:`MIT Licensed <mit>` format-agnostic tabular dataset library,
    >>> data = tablib.Dataset(headers=['First Name', 'Last Name', 'Age'])
    >>> for i in [('Kenneth', 'Reitz', 22), ('Bessie', 'Monke', 21)]:
    ...     data.append(i)
-      
 
-   >>> print data.json
+
+   >>> print(data.json)
    [{"Last Name": "Reitz", "First Name": "Kenneth", "Age": 22}, {"Last Name": "Monke", "First Name": "Bessie", "Age": 21}]
 
-   >>> print data.yaml
+   >>> print(data.yaml)
    - {Age: 22, First Name: Kenneth, Last Name: Reitz}
    - {Age: 21, First Name: Bessie, Last Name: Monke}
 
    >>> data.xlsx
    <censored binary data>
 
+   >>> data.df
+     First Name Last Name  Age
+   0    Kenneth     Reitz   22
+   1     Bessie     Monke   21
+
 
 Testimonials
 ------------