purescript
Add details on how Int is represented when compiling to Javascript
The documentation for Int in Prim says:
"A 32-bit signed integer. See the purescript-integers package for details of how this is accomplished when compiling to JavaScript."
I don't think this package really fulfills that promise at the moment. It would be nice to add some documentation about how that is handled when compiling to Javascript.
In a multi-compiler world maybe this package isn't the right place for that. In that case, perhaps we put the documentation somewhere else but it would still be nice if it existed.
One part of it is that bitwise operations cause a float 64 to be internally converted to int 32 by JS https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_operators#bitwise_operators
The rest (other than bitwise operators) is also unclear to me, i was wondering about it as well.
