Merge pull request realpython#19 from alex/patch-2

CPython slow, PyPy fast.

Author: Kenneth Reitz

docs/scenarios/speed.rst

@@ -1,7 +1,7 @@
 Speed
 =====
 
-Python isn't the fastest language around (yet)
+CPython, the most commonly used implementation of Python, is slow for CPU bound tasks. `PyPy`_ is fast.
 
 
 Context
@@ -53,4 +53,7 @@ Spanwing Processes
 
 
 Multiprocessing
----------------
+---------------
+
+
+.. _`PyPy`: http://pypy.org