Add a section in the README for environment variable setup and adjust the Cargo dependencies to match worker-build to prevent Action failures.

[afoim]

I made two changes:

1. Declared the environment variable configuration in the README. I have tested this, and these variables are required; otherwise, the project will not work.
2. Updated the version of wasm-bindgen in Cargo.toml to prevent GitHub Actions from throwing the following error:

error: 

it looks like the Rust project used to create this Wasm file was linked against
version of wasm-bindgen that uses a different bindgen format than this binary:

 rust Wasm file schema version: 0.2.103
     this binary schema version: 0.2.105 (f72a9d68d)

Currently the bindgen format is unstable enough that these two schema versions
must exactly match. You can accomplish this by either updating this binary or
the wasm-bindgen dependency in the Rust project.

You should be able to update the wasm-bindgen dependency with:

    cargo update -p wasm-bindgen --precise 0.2.105 (f72a9d68d)

don't forget to recompile your Wasm file! Alternatively, you can update the
binary with:

    cargo install -f wasm-bindgen-cli --version 0.2.103

if this warning fails to go away though and you're not sure what to do feel free
to open an issue at https://github.com/wasm-bindgen/wasm-bindgen/issues!

Error: Running the wasm-bindgen CLI

Caused by:
    failed to execute `wasm-bindgen`: exited with exit status: 1
      full command: "/home/runner/.cache/worker-build/wasm-bindgen-x86_64-unknown-linux-musl-0.2.105/wasm-bindgen" "/home/runner/work/warden-worker/warden-worker/target/wasm32-unknown-unknown/release/warden_worker.wasm" "--out-dir" "/home/runner/work/warden-worker/warden-worker/build" "--typescript" "--target" "module" "--out-name" "index" "--experimental-reset-state-function"