Add docs to userStartAudio + other utils

[davepagurek]

In the old p5.sound library, we had these docs: https://archive.p5js.org/reference/#/p5/userStartAudio

I think we still have it here, but just without doc comments:

p5.sound.js/src/Utils.js

Lines 17 to 19 in 064f415

	function userStartAudio() {
	ToneStart();
	}

It would maybe be good to add those docs + examples back (and possibly for the other utils in that file too, like getAudioContext)

cc @Qianqianye

[Qianqianye]

Thanks @davepagurek. Hi @ogbabydiesal, could you double check if we have any other missing documents besides userStartAudio?

[ogbabydiesal]

docs added 🤙