Update README.md

Author: erezrokah

README.md

@@ -44,7 +44,7 @@ allprojects {
 
 #### Android
 
-1. Open up `android/app/src/main/java/[...]/MainActivity.java`
+1. Open up `android/app/src/main/java/[...]/MainApplication.java`
   - Add `import io.rumors.reactnativefirebaseui.RNFirebaseUiPackage;` to the imports at the top of the file
   - Add `new RNFirebaseUiPackage()` to the list returned by the `getPackages()` method
 2. Append the following lines to `android/settings.gradle`: