We have a bunch of small grammatical nits and slightly awkward phrasings
present in our existing markdown files. This is a small pass over all of
them to fix those, and to provide some additional updated information
that has become more clear over time (like additional users of Luau, or
our leveraging something akin to the Minus 100 Points philosophy for
evaluating RFCs).

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Co-authored-by: Varun Saini <61795485+vrn-sn@users.noreply.github.com>