improving buy_btc_simple.py example

catalyst/examples/buy_btc.py

@@ -1,10 +0,0 @@
-from catalyst.api import order, record, symbol
-
-
-def initialize(context):
-    context.asset = symbol('btc_usd')
-
-
-def handle_data(context, data):
-    order(context.asset, 1)
-    record(btc=data.current(context.asset, 'price'))

catalyst/examples/buy_btc_simple.py

@@ -1,3 +1,24 @@
+'''
+	This is a very simple example referenced in the beginner's tutorial:
+	https://enigmampc.github.io/catalyst/beginner-tutorial.html
+
+	Run this example, by executing the following from your terminal:
+	catalyst run -f buy_btc_simple.py -x bitfinex --start 2016-1-1 --end 2017-9-30 -o buy_btc_simple_out.pickle
+
+	If you want to run this code using another exchange, make sure that 
+	the asset is available on that exchange. For example, if you were to run 
+	it for exchange Poloniex, you would need to edit the following line:
+
+		context.asset = symbol('btc_usdt')     # note 'usdt' instead of 'usd'
+
+	and specify exchange poloniex as follows:
+
+	catalyst run -f buy_btc_simple.py -x poloniex --start 2016-1-1 --end 2017-9-30 -o buy_btc_simple_out.pickle
+
+	To see which assets are available on each exchange, visit:
+	https://www.enigma.co/catalyst/status
+'''
+
 from catalyst.api import order, record, symbol
 
 def initialize(context):