route.md: Add wildcard example code

To developers completely new to axum, it helps a lot to give example
code on to get access to the variable path in a handler.

axum/src/docs/routing/route.md

@@ -60,6 +60,16 @@ Wildcard captures can also be extracted using [`Path`](crate::extract::Path).
 Note that the leading slash is not included, i.e. for the route `/foo/*rest` and
 the path `/foo/bar/baz` the value of `rest` will be `bar/baz`.
 
+Example:
+
+```rust
+let app = Router::new().route("/*key", get(handler));
+
+async fn handler(path: axum::extract::Path<String>) -> String {
+    path.0
+}
+```
+
 # Accepting multiple methods
 
 To accept multiple methods for the same route you can add all handlers at the