Apply suggestions from code review

Co-Authored-By: Eliza Weisman <eliza@buoyant.io>

tokio/src/runtime/builder.rs

@@ -177,7 +177,7 @@ impl Builder {
         self
     }
 
-    /// Set the name fn of threads spawned by the `Runtime`'s thread pool.
+    /// Sets a function used to generate the name of threads spawned by the `Runtime`'s thread pool.
     ///
     /// The default name fn is `|| "tokio-runtime-worker".into()`.
     ///
@@ -189,12 +189,12 @@ impl Builder {
     ///
     /// # pub fn main() {
     /// let rt = runtime::Builder::new()
-    /// .thread_name_fn(|| {
-    ///    static ATOMIC_ID: AtomicUsize = AtomicUsize::new(0);
-    ///    let id = ATOMIC_ID.fetch_add(1, Ordering::SeqCst);
-    ///    format!("my-pool-{}", id)
-    /// })
-    /// .build();
+    ///     .thread_name_fn(|| {
+    ///        static ATOMIC_ID: AtomicUsize = AtomicUsize::new(0);
+    ///        let id = ATOMIC_ID.fetch_add(1, Ordering::SeqCst);
+    ///        format!("my-pool-{}", id)
+    ///     })
+    ///     .build();
     /// # }
     /// ```
     pub fn thread_name_fn<F>(&mut self, f: F) -> &mut Self
@@ -482,7 +482,7 @@ impl fmt::Debug for Builder {
         fmt.debug_struct("Builder")
             .field("kind", &self.kind)
             .field("num_threads", &self.num_threads)
-            .field("thread_name_fn", &"<dyn Fn()->String+Send+Sync+'static>")
+            .field("thread_name_fn", &"<dyn Fn() -> String + Send + Sync + 'static>")
             .field("thread_stack_size", &self.thread_stack_size)
             .field("after_start", &self.after_start.as_ref().map(|_| "..."))
             .field("before_stop", &self.after_start.as_ref().map(|_| "..."))