Fix pod installation syntax

Running `pod install Firebase/Messaging` results in `[!] Unknown command: 'Firebase/Messaging'` using Cocoapods v1.3.1.
Also, there was a parse error in `HEADER_SEARCH_PATHS = "$(SRCROOT)/../node_modules/react-native/Libraries/PushNotificationIOS/**""$(SRCROOT)/../node_modules/react-native-fcm/ios";`, I was able to fix it by opening `APPNAME.xcodeproj/project.pbxproj`.

README.md

@@ -171,12 +171,24 @@ Notes:
 
 ### Pod approach:
 
-Make sure you have Cocoapods version > 1.0
+Make sure you have [Cocoapods](https://cocoapods.org/) version > 1.0
 
-Install the `Firebase/Messaging` pod:
+Configure the project:
 ```
 cd ios && pod init
-pod install Firebase/Messaging
+```
+
+(In case of syntax errors, `open YOURApp.xcodeproj/project.pbxproj` and fix them.)
+
+Edit the newly created `Podfile`:
+```diff
+  # Pods for YOURAPP
++ pod 'FirebaseMessaging'
+```
+
+Install the `Firebase/Messaging` pod:
+```
+pod install
 ```
 NOTE: you don't need to enable `use_frameworks!`. if you have to have `use_frameworks!` make sure you don't have `inherit! :search_paths`