Update README.md

README.md

 ```js
 
 RNFetchBlog
+    .config({
+        // DCIMDir is in external storage
+        path : dirs.DCIMDir + '/music.mp3'
+    })
     .fetch('GET', 'http://example.com/music.mp3')
     .then((res) => RNFetchBlob.fs.scanFile([ { path : res.path(), mime : 'audio/mpeg' } ]))
     .then(() => {
 
 If mime is null or undefined, then the mime type will be inferred from the file extension.
 
-**Download Notification and Visibiliy in Download App**
+**Download Notification and Visibiliy in Download App (Android Only)**
 
-Generally, when you store a file into 
+If you want to download success notification or make the stored file visible like the above. You have to add some options to `config`. 
 
 ```js
 RNFetchBlob.config({
   fileCache : true,
-  // android only options
+  // android only options, these options be a no-op on IOS
   addAndroidDownloads : {
     // Show notification when response data transmitted
     notification : true,
 .then(...)
 ```
 
-
 #### File Access
 
 File access APIs were made when developing `v0.5.0`, which helping us write tests, and was not planned to be a part of this module. However I realized that, it's hard to find a great solution to manage cached files, every one who use this moudle may need those APIs for there cases.