Sync PyPi package description with Github README

[jicruz96]

trafficstars

closes #3452

The reason your PyPi Project Page is out of sync is because of an out-dated hard-coded description in your setup.py file. To fix it:

• setup.py now uses the project README text for long_description
• All README image paths have been updated to their respective HTTP urls.

[jicruz96]

unrelated to this PR, I started a conversation in the Google Groups Gensim forum (as recommended by your contribution guidelines when opening new issues) asking if working on adding type hints to gensim would be welcome work, but I haven't gotten any response. Just pinging that again here.

[piskvorky]

setup.py now uses the project README text for long_description

IIRC setup.py (PyPI) used to required the RST format, whereas our README uses the Markdown format. That's why we kept two different descriptions, with just a stub (RST) for PyPI.

If that's no longer the case and setup.py now supports markdown (which it apparently does), that's great. That simplifies things. Thanks for the PR!