Update setup.py: add classifiers & python_requires (#2151)

* 📌 Update classifiers & add python_requires

* 👌 Allow Python version > 3

Author: opacam

setup.py

@@ -88,6 +88,7 @@ def recursively_include(results, directory, patterns):
       description='Android APK packager for Python scripts and apps',
       long_description=long_description,
       long_description_content_type='text/markdown',
+      python_requires=">=3.6.0",
       author='The Kivy team',
       author_email='kivy-dev@googlegroups.com',
       url='https://github.com/kivy/python-for-android',
@@ -114,6 +115,9 @@ def recursively_include(results, directory, patterns):
           'Operating System :: Android',
           'Programming Language :: C',
           'Programming Language :: Python :: 3',
+          'Programming Language :: Python :: 3.6',
+          'Programming Language :: Python :: 3.7',
+          'Programming Language :: Python :: 3.8',
           'Topic :: Software Development',
           'Topic :: Utilities',
           ],