Added link to Cache Invalidation demo app from FAQ (#6757)

Co-authored-by: Jon Harrell <4829245+jharrell@users.noreply.github.com>

Author: nurul3101

content/300-accelerate/600-faq.mdx

@@ -175,6 +175,8 @@ While you can increase these limits based on your subscription plan, it's *still
 
 As the cache needs to be cleared globally, it is difficult to provide a specific time frame. However, the cached data is eventually consistent and typically propagates to all PoPs within a few seconds. In very rare cases, it may take longer.
 
+Here is a [demo app](https://pris.ly/test-cache-invalidation) to test the time it takes to invalidate a cache query result.
+
 ## What is the difference between **Invalidate** and **Revalidate**?
 
 **Invalidate**: The cache entry is deleted, and new data will be fetched on the next request, causing a cache miss. This removes stale data but may lead to slower responses until the cache is repopulated.