DOC: jupyter notebook fix

docs/source/beginner-tutorial.rst

@@ -486,6 +486,10 @@ collect, the second argument is the unit (either ``'1d'`` for ``'1m'``
 but note that you need to have minute-level data for using ``1m``). This is
 a function we use in the ``handle_data()`` section:
 
+.. code-block:: python
+  
+  %load_ext catalyst
+
 .. code-block:: python
 
     %%catalyst --start 2016-4-1 --end 2017-9-30 -x bitfinex