Update arxiv link for AEC paper

[BertrandDecoster]

Description

The paper link is dead, because the paper was merged with the PZ paper

Jordan says it was merged into the pettingzoo paper and is a section there
https://arxiv.org/abs/2009.14471 updated arxiv link

https://discord.com/channels/961771112864313344/1131931827226021908/1131992209881837568

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

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

Just a doc change

[elliottower]

I ended up writing a bunch of more information myself today to make things abundantly clear, but thanks for the PR (if I had seen this I would've branched from it so you get some credit)
#1041

[elliottower]

Just closing as the other PR has much more information that I spent a long time writing out, so I think it should be sufficient