fixing link in doc comments

[JupiLogy]

Description

Many documentation comments in the env files are pointing to a now non-existent file (minigrid/minigrid.py). I have updated all of these to include a link to the new location of the index mappings.

Type of change

Please delete options that are not relevant.

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

Checklist:

(haven't done these due to changes being really straightforward and only in documentation)

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• 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

[pseudo-rnd-thoughts]

Thank you for fixing the links