REL: add long_description to setup.py

twine requires it for setting project description on PyPI.

Author: pavoljuhas

setup.py

@@ -137,6 +137,9 @@ def getversioncfg():
 
 versiondata = getversioncfg()
 
+with open(os.path.join(MYDIR, 'README.rst')) as fp:
+    long_description = fp.read()
+
 # define distribution
 setup_args = dict(
     name = "diffpy.srreal",
@@ -157,6 +160,8 @@ def getversioncfg():
     maintainer_email = "pavol.juhas@gmail.com",
     description = ("calculators for PDF, bond valence sum, and other "
                    "quantities based on atom pair interaction."),
+    long_description = long_description,
+    long_description_content_type = 'text/x-rst',
     license = 'BSD-style license',
     url = "https://github.com/diffpy/diffpy.srreal/",
     keywords = "PDF BVS atom overlap calculator real-space",