iOS Dynamic Links #70

I had trouble getting my app to build while following the documentation. I got lost between editing Info, not knowing what to add there and how to refer to it in AppDelegate.m.

Eventually, I got it to build like this:

#import "RNFirebaseLinks.h"
..
@implementation AppDelegate

static NSString *const CUSTOM_URL_SCHEME = @"applinks:APP_ID.app.goo.gl";
..
  [FIROptions defaultOptions].deepLinkURLScheme = CUSTOM_URL_SCHEME;
  [FIRApp configure];

About to test if it actually works. Not sure how to improve the docs.. should the Info.plist editing me elaborated on or should we define a const like above?