docs(service): minor language fixes to Service::call (#3449)

Author: Allan

src/service/service.rs

@@ -28,13 +28,13 @@ pub trait Service<Request> {
     type Future: Future<Output = Result<Self::Response, Self::Error>>;
 
     /// Process the request and return the response asynchronously.
-    /// call takes a &self instead of a mut &self because:
+    /// `call` takes `&self` instead of `mut &self` because:
     /// - It prepares the way for async fn,
-    ///   since then the future only borrows &self, and thus a Service can concurrently handle
+    ///   since then the future only borrows `&self`, and thus a Service can concurrently handle
     ///   multiple outstanding requests at once.
     /// - It's clearer that Services can likely be cloned
-    /// - To share state across clones you generally need Arc<Mutex<_>>
-    ///   that means you're not really using the &mut self and could do with a &self
-    /// To see the discussion on this see: <https://github.com/hyperium/hyper/issues/3040>
+    /// - To share state across clones, you generally need `Arc<Mutex<_>>`
+    ///   That means you're not really using the `&mut self` and could do with a `&self`.
+    /// The discussion on this is here: <https://github.com/hyperium/hyper/issues/3040>
     fn call(&self, req: Request) -> Self::Future;
 }