Feature Request: Support In-App Messaging #1112

Author: EddyVerbruggen

docs/IN_APP_MESSAGING.md

@@ -0,0 +1,44 @@
+<img src="https://raw.githubusercontent.com/EddyVerbruggen/nativescript-plugin-firebase/master/docs/images/features/inappmessaging.png" height="85px" alt="In-App Messaging"/>
+
+> Added in plugin version 8.2.0
+
+## In-App Messaging?
+Engage active app users with contextual messages.
+
+[Learn more here..](https://firebase.google.com/docs/in-app-messaging/)
+
+## Want to see a demo?
+Check out the (code of the) [Vue demo](demo-vue)!
+
+## Enabling Cloud Functions
+To add this feature to your project, either:
+
+* Remove `firebase.nativescript.json` from the root of the project and run `npm i`, or
+* Edit that file and add `"in_app_messaging": true`.
+
+In both cases, remove the `/platforms` folder afterwards so the required native library will be added upon the next build. 
+
+## API
+There's nothing you have to do code-wise if you only want to display messages.
+If you want to capture a 'button clicked' event however, read on.
+
+### `onMessageClicked`
+
+```typescript
+import { inappmessaging } from "nativescript-plugin-firebase/inappmessaging";
+
+inappmessaging.onMessageClicked(message => {
+  console.log("Clicked a button for Campaign: " + message.campaignName);
+});
+```
+
+### `onMessageImpression`
+You can also get notified if a message is being shown to a user:
+
+```typescript
+import { inappmessaging } from "nativescript-plugin-firebase/inappmessaging";
+
+inappmessaging.onMessageImpression(message => {
+  console.log("A message belonging to this campaign is being shown: " + message.campaignName);
+});
+```