Improve error message when example fails to run

cli/src/main.rs

@@ -84,10 +84,13 @@ fn main() -> io::Result<()> {
                 .expect("rustc failed to run");
 
             // Step 4: Run the compiled app
-            Command::new(cwd.join("app"))
-                .spawn()
-                .expect("./app failed to run");
-
+            Command::new(cwd.join("app")).spawn().unwrap_or_else(|err| {
+                panic!(
+                    "{} failed to run: {:?}",
+                    cwd.join("app").to_str().unwrap(),
+                    err
+                )
+            });
             Ok(())
         }
         None => {