[Updated] Document options when adding interceptors

posts/en/interceptors.md

@@ -6,7 +6,11 @@ next_title: 'Handling Errors'
 next_link: '/docs/handling_errors'
 ---
 
-You can intercept requests or responses before they are handled by `then` or `catch`.
+You can intercept requests or responses **before** they are handled by `then` or `catch`.
+
+The `use` function adds a handler to the list of handlers to be run when the Promise is fulfilled or rejected. The handler is defined by the fulfilled and rejected functions.
+
+There is an optional `options` object that can be passed in as the third parameter. `synchronous` if the synchronous option is true. The handler is defined as asynchronous if the synchronous option is false. If the synchronous option is not provided, the handler is defined as asynchronous. `runWhen` will control when the provided interceptor will run. Provide a function that will return true or false on whether it should run, defaults to always true.
 
 ```js
 // Add a request interceptor
@@ -16,7 +20,9 @@ axios.interceptors.request.use(function (config) {
   }, function (error) {
     // Do something with request error
     return Promise.reject(error);
-  });
+  },
+  { synchronous: true, runWhen: () => /* This function returns true */}
+);
 
 // Add a response interceptor
 axios.interceptors.response.use(function (response) {