docs: add quick start section to TanStack Start integration (#7729)

docs/content/docs/integrations/tanstack.mdx

@@ -7,6 +7,19 @@ This integration guide is assuming you are using TanStack Start.
 
 Before you start, make sure you have a Better Auth instance configured. If you haven't done that yet, check out the [installation](/docs/installation).
 
+## Quick Start
+
+You can create a new TanStack Start project with Better Auth integrated using the following command. This CLI sets up a project with an auth instance configured with the plugin and mounted handlers.
+
+```package-install
+npm create @tanstack/start
+
+◇  What add-ons would you like for your project?
+│  Better Auth
+```
+
+## Usage
+
 ### Mount the handler
 
 We need to mount the handler to a TanStack API endpoint/Server Route.