docs(web-analytics): add tip to explicitly track signup events in conversion goals intro

Author: inkeep[bot]

contents/docs/web-analytics/conversion-goals.mdx

@@ -12,6 +12,8 @@ A conversion goal is a key event or action you want users to do. It can be seen
 - Download
 - Form submission
 
+**Tip:** For signups, don't rely on autocapture – explicitly track a `user_signed_up` event. This ensures reliable conversion tracking even when your UI changes. See our guide on [capturing custom events](/docs/getting-started/send-events#2-capture-custom-events) for details.
+
 In web analytics, these are higher-level goals that work well in the overview. To dive deeper, visualize multiple steps, and use breakdowns, you can use [funnels](/docs/product-analytics/funnels). 
 
 ## How to set up a conversion goal