Include rnpm link step to get runnable build

I had to do an rnpm link to get the app to run correctly, which I believe is generally necessary, so updating README.md to include that step.

Author: jonathana

README.md

@@ -17,7 +17,13 @@ git clone [email protected]:dabit3/react-native-hackathon-starter.git
 npm i
 ```
 
-3 run project
+3 link dependencies for react-native
+
+```
+rnpm link
+```
+
+4 run project
 
 The API for React Native Elements is located [here](https://github.com/dabit3/React-Native-Elements).