doc(transport): improve connect_with_connector doc (#432)

Co-authored-by: Lucio Franco <luciofranco14@gmail.com>

tonic/src/transport/channel/endpoint.rs

@@ -234,6 +234,10 @@ impl Endpoint {
     }
 
     /// Connect with a custom connector.
+    ///
+    /// This allows you to build a [Channel](struct.Channel.html) that uses a non-HTTP transport.
+    /// See the `uds` example for an example on how to use this function to build channel that
+    /// uses a Unix socket transport.
     pub async fn connect_with_connector<C>(&self, connector: C) -> Result<Channel, Error>
     where
         C: MakeConnection<Uri> + Send + 'static,