IO<->Promise interop is confusing

[mlms13]

I've seen some confusion about how to work with promises when using Relude.IO on both Discord and Twitter. The interop helpers live in a different module than Relude.IO which is good for a future world where core parts of Relude could compile on native, but terrible for discoverability.

At the very least, we should improve the IO docs to tell people where to find the functions they need.