Fixing doc on accessing response with then/catch

Docs were suggesting that accessing the response with `catch` was the same as accessing it with `then`. Split the two cases and point to the Handling Errors section. Also mention the case where a rejection callback is specified as second parameter of `then`.

README.md

@@ -322,7 +322,7 @@ The response for a request contains the following information.
 }
 ```
 
-When using `then` or `catch`, you will receive the response as follows:
+When using `then`, you will receive the response as follows:
 
 ```js
 axios.get('/user/12345')
@@ -332,9 +332,11 @@ axios.get('/user/12345')
     console.log(response.statusText);
     console.log(response.headers);
     console.log(response.config);
-});
+  });
 ```
 
+When using `catch`, or passing a [rejection callback](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then) as second parameter of `then`, the response will be available through the `error` object as explained in the [Handling Errors](#handling-errors) section.
+
 ## Config Defaults
 
 You can specify config defaults that will be applied to every request.