docs: add context to useComposing hook

[work-in-progress-danny]

Description
I saw this new hook useComposing and thought

"You beauty, a hook that I can use when a user starts typing to have some nice side effects in React"

after a rabbit hole of a morning I realised, composition is a very specific thing that this hook is referring too. Just want to save people from the same head scratcher moment

example gif

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Latest commit: e952144

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[dylans]

Thanks... also not a bad idea for a different kind of hook!

[dylans]

I'm not sure why the static site is failing to build with this PR, I'll look when time permits.