Update README: Remove all mention of `run_game.py`

[doyled-it]

In the docs and in the README there are mentions of run_game.py which is no longer in the repo.

[doyled-it]

Also, add a line about versions <2.0.0 in the README

[doyled-it]

Also, make sure the README points to the GIFs' URL instead of a relative file location.

(Because PyPi)