Add comment for custom themes in styles.xml

Added a comment for custom themes in styles.xml

android-project/app/src/main/res/values/styles.xml

@@ -6,5 +6,6 @@
     <item name="android:windowDrawsSystemBarBackgrounds">true</item>
     <item name="android:statusBarColor">@android:color/transparent</item>
     <item name="android:navigationBarColor">@android:color/transparent</item>
+    <!-- Add custom themes here -->
     </style>
 </resources>