Update basic_usage.md

[Ricardicus]

Description

I was following the basic usage example from the documentation and ran into:

$ pip install gymnasium[box2d]                    
zsh: no matches found: gymnasium[box2d]

It turns out one needs to wrap that argument into a single string.
The gymnasium error message for DependencyNotInstalled does this:

gymnasium.error.DependencyNotInstalled: pygame is not installed, run `pip install "gymnasium[box2d]"`

So this is a minor documentation fix.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• [x ] Documentation only change (no code changed)

Screenshots

Checklist:

• 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
• [ x] 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

[Kallinteris-Andreas]

This is due to zsh Behaviour