docs: fix minor typos in pre-bundling guides

[Bertie690]

Explanation of tpyos

the large amount of requests create a network congestion on the browser side"

For obvious reasons, grammatical incorrectness is bad.

The pre-bundling is performed with Rolldown so it's typically very fast

The 2nd change is technically stylistic, but AFAIK it's "normal" to put a comma before a mid-sentence 'so'.