Update setup.py: add classifiers & python_requires

[opacam]

No description provided.

[AndreMiras]

Nice! Just curious isn't this redundant? Don't we only need python_requires="==3.*,>=3.6.0".
If you added it in case of Python 4, I would say keep it simple

[AndreMiras]

I think for a while we also didn't have it as like Django is doing, you still want to have people from Python2 to see this package when pip search-ing or pip install-ing, so then we can display an explicit message saying Python 2 is not supported.
See https://github.com/django/django/blob/3.0.5/setup.py tell me if it makes sense to you?

[opacam]

Mmmm...interesting...I did some research...

I think that pip search doesn't care about python version...for instance...I maintain a Python3 only package, never compatible with Python2. This project is named Cohen3 and here you have the first version I published at pipy. You will se that is classified as Python3, but here you have the pip2 search:

opacam@DEPOBOX:~$ pip2 search Cohen3
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. A future version of pip will drop support for Python 2.7. More details about Python 2 support in pip, can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support
Cohen3 (0.9.2)  - Cohen3 - DLNA/UPnP Media Server

And if you try to install a python3 only package, using the branch of this PR:

opacam@DEPOBOX:~$ pip2 install https://github.com/opacam/python-for-android/archive/feature-update-classifiers.zip --user
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. A future version of pip will drop support for Python 2.7. More details about Python 2 support in pip, can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support
Collecting https://github.com/opacam/python-for-android/archive/feature-update-classifiers.zip
  Downloading https://github.com/opacam/python-for-android/archive/feature-update-classifiers.zip
     / 2.0 MB 167 kB/s
ERROR: Package 'python-for-android' requires a different Python: 2.7.18 not in '==3.*,>=3.6.0'

[AndreMiras]

I think pip do care when searching and your project didn't have the Python classifier on the setup so I think that's why it appeared https://github.com/opacam/Cohen3/blob/0.8.0/setup.py
Either way I don't really mind as it was more a heads up and I think Django really does it for this reason
Edit: to make it clear, I'm talking about python_requires part
Edit: Check specifically the Note https://packaging.python.org/guides/distributing-packages-using-setuptools/#python-requires