Resolve "Add comments to all files"

Closes #67 (closed)

navigation/AuthStackScreen.js

@@ -6,6 +6,11 @@ import SignUpScreen from "../screens/SignUpScreen";
 
 const AuthStack = createStackNavigator();
 
+/**
+ * A stack navigator that contains the authentication screens. 
+ * 
+ * @returns the component
+ */
 const AuthStackScreen = () => (
   <AuthStack.Navigator
     screenOptions={{