doc: Adds a note on installing ios-deploy on MacOS 10.11.

doc/mobile.md

     npm install -g ios-deploy
     ```
 
+    You may need to add ```--unsafe-perm=true``` if you are running on [Mac OS 10.11 or greater](https://github.com/phonegap/ios-deploy#os-x-1011-el-capitan-or-greater).
+
 2. Build the app
 
     There are 2 ways to build the app: using the CLI or using Xcode.