Fix documentation for MethodRouter::into_make_service (#2176)

axum/src/routing/method_routing.rs

@@ -604,9 +604,10 @@ where
 }
 
 impl MethodRouter<(), Infallible> {
-    /// Convert the handler into a [`MakeService`].
+    /// Convert the router into a [`MakeService`].
     ///
-    /// This allows you to serve a single handler if you don't need any routing:
+    /// This allows you to serve a single `MethodRouter` if you don't need any
+    /// routing based on the path:
     ///
     /// ```rust
     /// use axum::{