specify react-native link module in readme

README.md

 For 0.29.2+ projects, simply link native packages via the following command (note: rnpm has been merged into react-native)
 
 ```
-react-native link
+react-native link rn-fetch-blob
 ```
 
 As for projects < 0.29 you need `rnpm` to link native packages
 Optionally, use the following command to add Android permissions to `AndroidManifest.xml` automatically
 
 ```sh
-RNFB_ANDROID_PERMISSIONS=true react-native link
+RNFB_ANDROID_PERMISSIONS=true react-native link rn-fetch-blob
 ```
 
 pre 0.29 projects