Update faq.mdx

new FAQ Q

Author: kathayl

src/content/docs/browser-rendering/faq.mdx

@@ -94,3 +94,6 @@ If you are still running into concurrency limits you can [request a higher limit
 ### Is there a limit to how many requests a single browser session can handle?
 
 No, there is not a fixed limit on the number of requests per browser session. A single browser can handle multiple requests as long as it stays within the available compute and memory limits.
+
+###  Do failed API calls, such as those that time out, add to billable browser hours?
+No. If a request to the Browser Rendering REST API fails with a waitForTimeout error, the browser session is not charged.