Doc formatting tweaks

Author: gaearon

docs/api/mixins/Navigation.md

@@ -36,14 +36,17 @@ this.replaceWith('/users/10?showAge=true');
 ### `goBack()`
 
 Programmatically go back to the last route and remove the most recent
-entry from the browser history. Return false if it's the first entry in the app history, true otherwise.
+entry from the browser history. Returns `true` unless it's the first entry
+in the app history.
 
 #### Example
 
 ```js
 this.goBack();
 ```
-If you want to make sure there is an history entry
+
+If you want to make sure there was a history entry to go back to, use the return value:
+
 ```js
 if (!this.goBack()) {
   this.transitionTo('/otherpage')