fix: nushell integration after nushell language change

[heiytor]

Summary

I encountered an issue while setting up asdf in my Nushell. The error message stated that the let-env call is deprecated and should be replaced with $env.<environment variable>. I noticed that the Nushell documentation has not been updated to reflect this change. To resolve this issue, I made the necessary changes and improvements to the Nushell & Git documentation in the getting started section for both English and Brazilian users.

This pull request addresses the following:

1. Replaces all instances of let-env with $env.PATH to fix the deprecation issue.
2. Improved the Nushell & Git documentation to reflect the correct usage for setting environment variables. I don't have macOS or Arch, so I didn't change the respective documentation.

Fixes: #1609

Changes Made

• Replaced all let-env calls with $env.PATH to comply with the deprecation.
  
• Updated the Nushell & Git documentation in the getting started section for both English and Brazilian users.

Thank you for considering this pull request. I'm looking forward to your feedback!

[hyperupcall]

Thank you for starting this!

Did you run the tests locally? They contain uses of let-env as well and they also show the deprecation notices.

[heiytor]

Hello.

I ended up forgetting to do the tests. I'll do another commit to resolve this, also review the semantic-pr.

[jthegedus]

as with #1624 this is still broken as the Nushell language has changed again.

[jthegedus]

Closed in #1624

Thanks for raising this PR @heiytor Apologies for being AFK and not getting to merging this before yet another Nushell language change. Your contributions are appreciated despite not being merged 🙇