fix broken links

[xixinzhang]

Description

Fix some broken links to the code and markdown file in documentation, as the directory tutorials/EnvironmentCreation is renamed to tutorials/CustomEnvironment and the directory docs/tutorials/environmentcreation is renamed to docs/tutorials/custom_environment in #1082.

Type of change

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

Screenshots

An example of broken links to the code of the tutorial in https://pettingzoo.farama.org/tutorials/custom_environment/3-action-masking/:

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

[elliottower]

Oh shoot my fault for missing this, I searched and replaced through files to fix all the other references I’m pretty sure but I guess I missed this. Thanks for the help.

[elliottower]

Kind of rushed to get the hotfix out cause ppl were complaining about shimmy being broken