add read me for the new version number change.

Test Plan: n/a

Differential Revision: https://phabricator.intern.facebook.com/D17123217

Android/README.md

@@ -61,6 +61,8 @@ You must also modify the contents.json file in SampleStickerApp/app/src/main/ass
 * `identifier`: The identifier should be unique and can be alphanumeric: a-z, A-Z, 0-9, and the following characters are also allowed "_", "-", "." and " ". The identifier should be less than 128 characters.
 * `publisher`: name of the publisher of the pack (128 characters max)
 * Replace the "image_file" value with the file name of your sticker image. It must have both the file name and extension. The ordering of the files in the JSON will dictate the ordering of your stickers in your pack. 
+* `image_data_version` : an overall representation of the version of the stickers and tray icon. When you update stickers or tray icon in your pack, please update this string, this will tell WhatsApp that the pack has new content and update the stickers on WhatsApp side.
+* `avoid_cache` : this tells WhatsApp that the stickers from your pack should not be cached. By default, you should keep it false. Exception is that if your app updates stickers without user actions, you can keep it true, for example: your app provides clock sticker that updates stickers every minute.
 * `android_play_store_link` and `ios_app_store_link` (optional fields): here you can put the URL to your sticker app in the Google Play Store and Apple App Store (if you have an iOS version of your sticker app). If you provide these URLs, users who receive a sticker from your app in WhatsApp can tap on it to view your sticker app in the respective App Stores. On Android, the URL follows the format https://play.google.com/store/apps/details?id=com.example where "com.example" is your app's package name.
 * `emojis` (optional): add up to a maximum of three emoji for each sticker file. Select emoji that best describe or represent that sticker file. For example, if the sticker is portraying love, you may choose to add a heart emoji like 💕. If your sticker portrays pizza, you may want to add the pizza slice emoji 🍕. In the future, WhatsApp will support a search function for stickers and tagging your sticker files with emoji will enable that. The sticker picker/tray in WhatsApp today already categorizes stickers into emotion categories (love, happy, sad, and angry) and it does this based on the emoji you tag your stickers with.
 
@@ -162,3 +164,10 @@ The result is in a row corresponding to the column named `result`. The value wil
 Note that a pack can be added to either the main WhatsApp app, WhatsApp Business, or both. It is recommended you continue to present a button to add the pack to WhatsApp if the sticker pack is not added to one or more of the apps. Refer to the class [WhitelistCheck](app/src/main/java/com/example/samplestickerapp/WhitelistCheck.java) for sample logic.
 
 Your app can only query whether the packs it provides have been added and it can't check for information about sticker packs from other apps.
+
+### Update image data version
+In a recent update, image data version (image_data_version in contents.json) was introduced, this is a way to tell WhatsApp whether your app has new content or not.
+
+If you update your stickers, add new stickers to a pack, you should update this value.
+
+If your app allows users to add/update/delete stickers from a pack, you should update the value after users have made changes.