Add specifics around DeepSpeed docs

[SeanNaren]

What does this PR do?

Some small doc fixes to be more specific when to use DeepSpeed.

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[codecov]

Codecov Report

Merging #6142 (09967e1) into master (0456b45) will decrease coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #6142   +/-   ##
======================================
- Coverage      91%     91%   -0%     
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  Files         160     160           
  Lines       11423   11423           
======================================
- Hits        10434   10405   -29     
- Misses        989    1018   +29