DOC: documented 4 example algorithms

catalyst/examples/README.rst

@@ -0,0 +1,3 @@
+An overview of most of the trading strategies in this folder can be found in the 
+`Examples Algorithms <https://enigmampc.github.io/catalyst/example-algos.html>`_
+section of our documentation website.

docs/source/beginner-tutorial.rst

@@ -546,6 +546,7 @@ only bought bitcoin every chance it got.
       sudo apt install python-tk
 
 
+.. _history:
 
 Access to previous prices using ``history``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~