Fix README.rst for PyPi

Add long_description_content_type in setup.py, fix incorrectly
matched up title underlines in README.rst, and fix incorrect entry in
MANIFEST.in that was forgotten when the README was renamed in 06296bf.

MANIFEST.in

@@ -1,4 +1,4 @@
-include README.md
+include README.rst
 include LICENSE
 include requirements.txt
 include discord/bin/*.dll

README.rst

@@ -11,7 +11,7 @@ discord.py is an API wrapper for Discord written in Python.
 This was written to allow easier writing of bots or chat logs. Make sure to familiarise yourself with the API using the `documentation <http://discordpy.rtfd.org/en/latest>`__.
 
 Breaking Changes
----------------
+----------------
 
 The discord API is constantly changing and the wrapper API is as well. There will be no effort to keep backwards compatibility in versions before ``v1.0.0``.
 
@@ -53,7 +53,7 @@ Please note that on Linux installing voice you must install the following packag
 * python-dev (e.g. ``python3.5-dev`` for Python 3.5)
 
 Quick Example
-------------
+-------------
 
 .. code:: py
 

setup.py

@@ -50,6 +50,7 @@ setup(name='discord.py',
       license='MIT',
       description='A python wrapper for the Discord API',
       long_description=readme,
+      long_description_content_type="text/x-rst",
       include_package_data=True,
       install_requires=requirements,
       extras_require=extras_require,