Make an example using html_playground_url in playground.md

Author: HosseinAssaran

src/meta/playground.md

@@ -39,6 +39,13 @@ button that says "Run", which opens the code sample up in a new tab in Rust
 Playground. This feature is enabled if you use the `#[doc]` attribute called
 [`html_playground_url`][html-playground-url].
 
+```
+#![doc(html_playground_url = "https://play.rust-lang.org/")]
+//! ```
+//! println!("Hello Wolrd");
+//! ```
+```
+
 ### See also:
 
 - [The Rust Playground][rust-playground]