Add a project for testing async feature

hello-async/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "hello-async"
+version = "0.1.0"

hello-async/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "hello-async"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

hello-async/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}

rust-exercises.code-workspace

@@ -1,5 +1,8 @@
 {
     "folders": [
+        {
+            "path": "./hello-async"
+        },
         {
             "path": "./add"
         },