add cocoa-lumberjack install step

Author: chestercharles

help/INSTALL-IOS.md

@@ -5,11 +5,13 @@
 
 ```shell
 yarn add react-native-background-geolocation
+yarn add cocoa-lumberjack
 ```
 
 ### With `npm`
 ```shell
 npm install react-native-background-geolocation --save
+npm install cocoa-lumberjack --save
 ```
 
 - In the XCode's **`Project navigator`**, right click on project's name ➜ **`Add Files to <...>`**