Adding the GameBoyLearning Environment to the documentation since it is based on Gymnasium

[edofazza]

Hi,

I was wondering if adding GLE to the documentation in External Environments could be of interest. Here is the GitHub repo: https://github.com/edofazza/GameBoyLearningEnvironment
and the paper: https://ieeexplore.ieee.org/document/11020792

Thanks
Best

[blayyyyyk]

This is really cool!