[deepspeed doc] install issues + 1-gpu deployment (#9582)

* [doc] install + 1-gpu deployment

* Apply suggestions from code review

Co-authored-by: Lysandre Debut <[email protected]>
Co-authored-by: Sylvain Gugger <[email protected]>

* improvements

Co-authored-by: Lysandre Debut <[email protected]>
Co-authored-by: Sylvain Gugger <[email protected]>