doc: Use absolute url in prerequisites index

docs/src/prerequisites/index.md

@@ -2,8 +2,8 @@
 
 To run `wasm-pack` you'll need to have both Rust and npm installed and configured.
 
-- [Rust](./prerequisites/rust.html)
-- [npm](./prerequisites/npm.html)
+- [Rust](/wasm-pack/book/prerequisites/rust.html)
+- [npm](/wasm-pack/book/prerequisites/npm.html)
 
 In the future, we intend to rewrite the npm registry client bits so that the need
 for a Node runtime is eliminated. If you're excited about that work- you should