fix: added ask fern link

Author: Kapil Gowru

fern/products/ask-fern/ask-fern.yml

@@ -4,7 +4,7 @@ navigation:
       - page: What is Ask Fern?
         path: ./pages/getting-started/what-is-ask-fern.mdx
       - link: Customer showcase
-        href: https://buildwithfern.com/customers
+        href: https://buildwithfern.com/showcase#ask-fern-customers
   - section: Configuration
     contents:
       - page: Custom prompting