Adding note about RNPM install prompt

Author: lostintangent

README.md

@@ -209,7 +209,9 @@ In order to accomodate as many developer preferences as possible, the CodePush p
 
     *Note: If you don't already have RNPM installed, you can do so by simply running `npm i -g rnpm` and then executing the above command.*
     
-2. (Only needed in v1.8.0+ of the plugin) In your `android/app/build.gradle` file, add the `codepush.gradle` file as an additional build task definition underneath `react.gradle`:
+2. If you're using RNPM >=1.6.0, you will be prompted for the deployment key you'd like to use. If you don't already have it, you can retreive this value by running `code-push deployment ls <appName> -k", or you can choose to ignore it (by simply hitting `<ENTER>`) and add it in later. To get started, we would recommend just using your `Staging` deployment key, so that you can test out the CodePush end-to-end.
+
+3. (Only needed in v1.8.0+ of the plugin) In your `android/app/build.gradle` file, add the `codepush.gradle` file as an additional build task definition underneath `react.gradle`:
     
     ```gradle
     ...