sdist: Fix source distribution including missing file. Fixes #11

Manually tested on Ubuntu 15.04 with gcc (Ubuntu 5.2.1-22ubuntu2) 5.2.1 20151010:

$ pip install cmake-python-distributions/dist/cmake-0.1.0.post4.dev0+g1645a2a.tar.gz
Processing ./cmake-python-distributions/dist/cmake-0.1.0.post4.dev0+g1645a2a.tar.gz
Building wheels for collected packages: cmake
  Running setup.py bdist_wheel for cmake ... done
  Stored in directory: /home/jcfr/.cache/pip/wheels/b9/09/62/5e4e26020faf8f8e20b8f638e81dc761f8068532c1c6bc45f8
Successfully built cmake
Installing collected packages: cmake
Successfully installed cmake-0.1.0.post4.dev0+g1645a2a

Author: jcfr

MANIFEST.in

@@ -1,5 +1,7 @@
 include CMakeLists.txt
 include requirements-dev.txt
+include HISTORY.rst
+include README.rst
 
 recursive-include src *
 include versioneer.py