Update links to WASI docs in time.rs module
Update links to WASI docs in time.rs module

Since the docs for the WASI API are now evolving in [WebAssembly/WASI] repo,
I thought it might be useful to update the links in the docs to point to that location
instead of using the outdated `CraneStation/wasmtime` destination.

[WebAssembly/WASI]: https://github.com/WebAssembly/WASI
graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust