DOC: Reference example in quickstart to keep it up-to-date.

Fix the quickstart docs by including the example so that it's
always up-to-date.

docs/quickstart.rst

@@ -8,48 +8,7 @@ Dual-Moving Average Example
 The following code implements a simple dual moving average algorithm
 and tests it on data extracted from yahoo finance.
 
-.. code-block:: python
-
-    from zipline.algorithm import TradingAlgorithm
-    from zipline.transforms import MovingAverage
-    from zipline.utils.factory import load_from_yahoo
-
-    class DualMovingAverage(TradingAlgorithm):
-        """Dual Moving Average algorithm.
-        """
-        def initialize(self, short_window=200, long_window=400):
-            # Add 2 mavg transforms, one with a long window, one
-            # with a short window.
-            self.add_transform(MovingAverage, 'short_mavg', ['price'],
-                            market_aware=True,
-                            days=short_window)
-
-            self.add_transform(MovingAverage, 'long_mavg', ['price'],
-                            market_aware=True,
-                            days=long_window)
-
-            # To keep track of whether we invested in the stock or not
-            self.invested = False
-
-            self.short_mavg = []
-            self.long_mavg = []
-
-
-        def handle_data(self, data):
-            if (data['AAPL'].short_mavg['price'] > data['AAPL'].long_mavg['price']) and not self.invested:
-                self.order('AAPL', 100)
-                self.invested = True
-            elif (data['AAPL'].short_mavg['price'] < data['AAPL'].long_mavg['price']) and self.invested:
-                self.order('AAPL', -100)
-                self.invested = False
-
-            # Save mavgs for later analysis.
-            self.short_mavg.append(data['AAPL'].short_mavg['price'])
-            self.long_mavg.append(data['AAPL'].long_mavg['price'])
-
-    data = load_from_yahoo()
-    dma = DualMovingAverage()
-    results = dma.run(data)
-
-You can find other examples in the zipline/examples directory.
+.. include:: ../zipline/examples/dual_moving_average.py
+   :literal:
 
+You can find other examples in `the zipline/examples directory <https://github.com/quantopian/zipline/tree/master/zipline/examples>`_.