[docs] Typos - Single GPU efficient training features (#38964)
* Typos
- corrected bf16 training argument
- corrected header for SDPA
* improved readability for SDPA suggested by @stevhliu
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
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Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>