Merge pull request #4297 from NativeScript/fatme/preview-help

fix: add preview to html's docs

Author: Fatme

docs/man_pages/index.md

@@ -27,6 +27,7 @@ Command | Description
 Command | Description
 ---|---
 [create](project/creation/create.html) | Creates a new project for native development with NativeScript.
+[preview](project/testing/preview.html) | Generates a QR code that can be scanned by the NativeScript PlayGround app.
 [init](project/creation/init.html) | Initializes an existing project for native development with NativeScript.
 [platform add `<Platform>`](project/configuration/platform-add.html) | Configures the current project to target the selected platform.
 [platform list](project/configuration/platform.html) | Lists all platforms that the project currently targets.