Fix the long description for new pypi

For the old pypi our project description was automatically read in from
`README.rst`. This is no longer the case:
https://pypi.org/project/Axelrod/

I believe this fixes it.

Author: drvinceknight

setup.py

@@ -7,6 +7,10 @@
         if "hypothesis" not in library:  # Skip: used only for dev
             requirements.append(library)
 
+# Read in long description
+with open("README.rst", "r") as f:
+    long_description = f.read()
+
 # Read in the version number
 exec(open('axelrod/version.py', 'r').read())
 
@@ -20,6 +24,8 @@
     url='http://axelrod.readthedocs.org/',
     license='The MIT License (MIT)',
     description='Reproduce the Axelrod iterated prisoners dilemma tournament',
+    long_description=long_description,
+    long_description_content_type='text/x-rst',
     include_package_data=True,
     package_data={
         '': ['axelrod/data/*.csv'],