updates contributing

Author: Phil Cummins

CONTRIBUTING.md

@@ -21,7 +21,15 @@ switch.
 ### Prerequisites
 
 - Tools needed to build [CPython](https://github.com/python/cpython) (Make, Clang, etc.)
-- [Rust](https://rustup.rs/) stable 1.81.0
+- [Rust](https://rustup.rs/) stable 1.81.0 or later, including the `wasm32-wasip1` and `wasm32-unknown-unknown` targets
+  - Note that we currently use the `-Z build-std` Cargo option to build the `componentize-py` runtime with position-independent code (which is not the default for `wasm32-wasip1`) and this requires using a recent nightly build of Rust.
+  
+For Rust, something like this should work once you have `rustup`:
+
+```shell
+rustup update
+rustup target add wasm32-wasip1 wasm32-unknown-unknown
+```
 
 ### Building and Running