Include license file into sdist

[nicoddemus]

Hi,

I'm about to create a conda package for this project, but noticed that the license file is missing from the source distribution.

By adding a MANIFEST.in file the license is included:

creating setuptools-markdown-0.2
creating setuptools-markdown-0.2\setuptools_markdown.egg-info
copying files to setuptools-markdown-0.2...
copying LICENSE-MIT -> setuptools-markdown-0.2
copying MANIFEST.in -> setuptools-markdown-0.2
copying README.rst -> setuptools-markdown-0.2
copying setup.cfg -> setuptools-markdown-0.2
copying setup.py -> setuptools-markdown-0.2

[msabramo]

Thanks!