Add frontend screenshot to initialize-sentry-frontend

Author: Alex Krawiec

docs/product/sentry-basics/distributed-tracing/img/frontend-screenshot.png

@@ -121,6 +121,7 @@ In the `tracing-tutorial-frontend` project folder:
    The sample app should be running at [http://localhost:3000/](http://localhost:3000/) or the URL output in your terminal in the last step. You should see a sample e-commerce page; the buttons on this page won't work correctly and will trigger an uncaught runntime error until you get your backend up and running.
 
    {/* ADD SCREENSHOT HERE */}
+   ![img/frontend-screenshot.png](img/frontend-screenshot.png)
 
 
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