Support Procgen Environments

[vwxyzjn]

Problem Description

Procgen Environments (https://github.com/openai/procgen) are new environments to test out the generalization ability of agents. It would be nice to include some of the games into the Open RL Benchmark (http://benchmark.cleanrl.dev/)

This is a good first issue for contributors. I think contributors can simply modify the network model slightly (

cleanrl/cleanrl/ppo_atari_visual.py

Line 514 in db00739

self.network = nn.Sequential(

) to handle the Procgen Environments.