Add a tutorial for async

[rom1504]

We need a tutorial detailing all the ways to use async with mineflayer
In particular how to do loop with either callback, promise or async/await
https://github.com/PrismarineJS/mineflayer/blob/master/docs/tutorial.md#callbacks is not enough

This is the most recurring question in discord, people don't get it

cc @Naomi-alt @wvffle if you're interested

[wvffle]

I suggest that for now, we should focus on callbacks for now.

I have pretty much no spare time to work on #984 but we should publish a guide for async/await only after it gets merged.

[rom1504]

People can always promisify a few methods themselves if they are more comfortable with promises