add download_url

Author: matteoaldeghi

setup.py

@@ -76,6 +76,7 @@ def readme():
       author='Daniel Seeliger',
       author_email='[email protected]',
       url='https://github.com/deGrootLab/pmx',
+      download_url="https://github.com/deGrootLab/pmx/releases/latest",
       license='GPL 3',
       packages=['pmx'],
       include_package_data=True,