docs(quickstart): add login and no-api guidance for CLI setup

[LarytheLord]

Summary

• add the missing codecarbon login step right after codecarbon config in Quickstart
• document a clear no-auth path for local usage with codecarbon monitor --no-api
• refresh generated docs artifacts (docs/usage.html, _sources, searchindex.js)
• improve wording around API example (localhost:8008) and fix grammar

Why

Issue #928 reports that Quickstart does not mention authentication, while codecarbon config users are prompted for login-related details.

This update makes the onboarding flow explicit for both cases:

1. API-backed usage (codecarbon login)
2. local-only usage (--no-api)

Closes #928.

[SaboniAmine]

Hello,
Thanks for your contribution!
We are currently migration our documentation system to a new tool, would it be ok if we ask you to port your additions to the new format (which will be markdown) ? We plan to have it merged before this week end.