Update Rust instructions, add a link to wasi-sysroot.

docs/WASI-documents.md

@@ -9,6 +9,8 @@ For specifics on the API, see the [API documentation](https://github.com/CraneSt
 Additionally, a C header file describing the WASI API is
 [here](https://github.com/CraneStation/wasi-sysroot/blob/wasi/libc-bottom-half/headers/public/wasi/core.h).
 
+The WASI libc repository is [wasi-sysroot](https://github.com/CraneStation/wasi-sysroot/).
+
 For some discussion of capability-based design, see the [Capabilities document](WASI-capabilities.md).
 
 For some discussion of WASI's design inspiration, see the [Background document](WASI-background.md).
@@ -19,4 +21,3 @@ For some ideas of things that we may want to change about WASI in the
 short term, see the [possible changes](WASI-some-possible-changes.md) document.
 For longer-term ideas, see the [possible future features](WASI-possible-future-features.md)
 document.
-

docs/WASI-intro.md

@@ -26,9 +26,12 @@ toolchains will be able to implement WASI as well!
 
 ### Rust
 
-To install a WASI-enabled Rust toolchain, follow the instructions here:
+To install a WASI-enabled Rust toolchain:
 
-https://github.com/alexcrichton/rust/releases/tag/wasi3
+```
+rustup target add wasm32-unknown-wasi --toolchain nightly
+cargo +nightly build --target wasm32-unknown-wasi
+```
 
 Until now, Rust's WebAssembly support has had two main options, the
 Emscripten-based option, and the wasm32-unknown-unknown option. The latter