docs: ✏️ update stale example of wasm decoder (bytecodealliance#1884)

crates/wasm-encoder/README.md

@@ -36,7 +36,7 @@ let mut module = Module::new();
 let mut types = TypeSection::new();
 let params = vec![ValType::I32, ValType::I32];
 let results = vec![ValType::I32];
-types.function(params, results);
+types.ty().function(params, results);
 module.section(&types);
 
 // Encode the function section.