New Example - Firebase Google Authentication (#106)

* Added the firebase+google_authentication example

* Modified Readme.md

firebase_google_authentication/android/build.gradle

@@ -0,0 +1,30 @@
+buildscript {
+    ext.kotlin_version = '1.3.50'
+    repositories {
+        google()
+        jcenter()
+    }
+
+    dependencies {
+        classpath 'com.android.tools.build:gradle:4.1.0'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+        classpath 'com.google.gms:google-services:4.3.10'
+    }
+}
+
+allprojects {
+    repositories {
+        google()
+        jcenter()
+    }
+}
+
+rootProject.buildDir = '../build'
+subprojects {
+    project.buildDir = "${rootProject.buildDir}/${project.name}"
+    project.evaluationDependsOn(':app')
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}