Reflex.Network: improve haddocks

[endgame]

• Replace reference to deprecated function with its replacement
• Normalise comment formatting
• Suggest how to flatten the result of networkHold

[alexfmpe]

*promptly ? That doesn't sound like something we want to recommend outside of very specific situations. I can only remember using it once in 5+ years

[endgame]

I haven't used networkHold much at all, but the previous version of the docs referenced a ...Promptly function. I think otherwise you miss any event firings from the frame that swaps the network in, and that's usually something I want (to capture).

[ali-abrar]

Agree we should rethink the use of promptly here, but that isn't new to this PR.