docs(tanstackstart-react): Add source maps quickstart instructions

Author: nicohrubec

docs/platforms/javascript/guides/tanstackstart-react/index.mdx

@@ -226,11 +226,17 @@ const route = createRoute({
 })
 ```
 
-## Step 4: Avoid Ad Blockers With Tunneling (Optional)
+## Step 4: Add Readable Stack Traces to Errors (Optional)
+
+The stack traces in your Sentry errors probably won't look like your actual code. To fix this, upload your source maps to Sentry. 
+
+Since TanStack Start uses Vite, you can use the Sentry Vite plugin to automatically upload source maps. Follow the [Vite source maps guide](/platforms/javascript/sourcemaps/uploading/vite/) to set this up.
+
+## Step 5: Avoid Ad Blockers With Tunneling (Optional)
 
 <PlatformContent includePath="getting-started-tunneling" />
 
-## Step 5: Verify
+## Step 6: Verify
 
 Let's test your setup and confirm that Sentry is working correctly and sending data to your Sentry project.