Fix minor grammatical corrections in docs

[aakashapoorv]

What does this PR do?

Fixes spelling and grammar corrections.

Changes Made:

Original	Correction	Summary of Change	Fixed
pipepling	pipelining	Corrected spelling error	Spelling correction in pipeline_parallelism.rst
falls (falls into two categories)	fall (fall into two categories)	Corrected verb for subject agreement	Grammar correction in oss_sdp_fsdp.rst

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• Did you write any new necessary tests?
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