doc: firebase-messaging instructions

Author: fabriziomoscon

README.md

@@ -86,6 +86,8 @@ To allow the library to show heads up notifications you must add the following l
     </application>
 ```
 
+Firebase Messaging 19.0.+ is imported by this module, so there is no need to import it in your app.
+
 Previously, in order to launch the app when receiving a call, the flow was:
 
 1. the module would launch the app

android/build.gradle

@@ -58,7 +58,7 @@ dependencies {
     implementation 'com.twilio:voice-android:5.0.2'
     implementation "com.android.support:appcompat-v7:$supportLibVersion"
     implementation 'com.facebook.react:react-native:+'
-    implementation 'com.google.firebase:firebase-messaging:17.6.+'
+    implementation 'com.google.firebase:firebase-messaging:19.0.+'
     implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'
     testImplementation 'junit:junit:4.12'
 }