Confusing syntax in API documentation

Looking at https://github.com/WebAssembly/WASI/blob/master/phases/snapshot/docs.md

For example, the function environ_sizes_get is shown as environ_sizes_get() -> (errno, size, size). This looks like it's returning three values, but if I compile a simple program to WASI this is the type of the function:

  (type (;3;) (func (param i32 i32) (result i32)))
  ...
  (import "wasi_snapshot_preview1" "environ_sizes_get" (func $__wasi_environ_sizes_get (type 3)))

So it's actually taking two args and returning one value.

I have no idea what the args are, I'm guessing they're memory locations to return values, first one is for errno, second one is for the first size, but I'm not sure. It'd be good to describe the syntax in the API docs.

Start with phases/snapshot/docs.md and inspect the environ_sizes_get entry alongside the issue's generated WASI type. Determine how the documented notation represents parameters, return values, and memory locations, then update the API documentation so the function signature and argument roles are unambiguous.