Expand AEC documentation significantly (comparison with EFGs/POSGs, info from PettingZoo paper)

[elliottower]

A user asked for more info about AEC envs because the original paper got taken down (combined with the PettingZoo paper), so I figure the page should have an about section in case someone else gets confused. I think it's also good to have examples showing how we have implemented the various design goals stated in the paper, with links to example environments to check out, etc.

Description

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Fixes # (issue), Depends on # (pull request)

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

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Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have run pytest -v and no errors are present.
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I solved any possible warnings that pytest -v has generated that are related to my code to the best of my knowledge.
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes