Add README to setup.py description

[djhoese]

The PyPI page for satpy does not include a description. From the information on the project settings page on PyPI it should come from the description field in the setup.py:

To set the 'satpy' description, author, links, classifiers, and other details for your next release, use the setup() arguments in your setup.py file. Updating these fields will not change the metadata for past releases. See the Python Packaging User Guide for more help.

https://pypi.org/project/satpy/

I think we should edit the setup.py to read the README.rst file and put it in the description field of the setup call. However, that doesn't explain why the current description 'Meteorological post processing package' isn't the current description of the package. Any ideas?

[djhoese]

Ah it must be the long_description https://packaging.python.org/tutorials/packaging-projects/#creating-setup-py