docs: add docs for previewQrCodeService in PublicApi.md

Author: Fatme

PublicAPI.md

@@ -64,7 +64,7 @@ const tns = require("nativescript");
 	* [deviceLost](#devicelost)
 	* [deviceLog](#devicelog)
 * [previewQrCodeService](#previewqrcodeservice)
-	* [getPlaygroundAppQrCode](#getplaygroundappqrCode)
+	* [getPlaygroundAppQrCode](#getplaygroundappqrcode)
 
 ## Module projectService
 
@@ -1409,6 +1409,21 @@ tns.previewDevicesService.on("deviceLogData", (device, message) => {
 });
 ```
 
+## previewQrCodeService
+The `previewQrCodeService` exposes methods for getting information about the QR of the Playground app and deployed app in Preview app.
+
+### getPlaygroundAppQrCode
+Returns information used to generate the QR code of the Playground app.
+
+* Usage:
+```TypeScript
+tns.previewQrCodeService.getPlaygroundAppQrCode()
+	.then(result => {
+		console.log("QR code data for iOS platform: " + result.ios);
+		console.log("QR code data for Android platform: " + result.android);
+	});
+```
+
 ## How to add a new method to Public API
 CLI is designed as command line tool and when it is used as a library, it does not give you access to all of the methods. This is mainly implementation detail. Most of the CLI's code is created to work in command line, not as a library, so before adding method to public API, most probably it will require some modification.
 For example the `$options` injected module contains information about all `--` options passed on the terminal. When the CLI is used as a library, the options are not populated. Before adding method to public API, make sure its implementation does not rely on `$options`.