feat(users/kranzes): add wasm-hello-world

This can be used as a reference for how to build a wasm project with
crate2nix.

Change-Id: Ib4d0db6bf24d8f1dec4734d5f1e8de19212a54cd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11859
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

users/kranzes/wasm-hello-world/src/lib.rs

@@ -0,0 +1,11 @@
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+extern "C" {
+    fn alert(s: &str);
+}
+
+#[wasm_bindgen]
+pub fn hello_world() {
+    alert("Hello World!");
+}