docs: add warning about captcha domains limit (#2107)

* docs: add warning about captcha domains limit

* use relative url

* chore: remove admonition

---------

Co-authored-by: vinckr <[email protected]>

Author: pcaillaudm

docs/kratos/concepts/security.mdx

@@ -79,12 +79,16 @@ credential stuffing, brute force and other automated attacks.
 #### Prerequisites
 
 Before proceeding, ensure you are on a plan that supports this feature. If you need CAPTCHA support, please
-[contact us](https://www.ory.sh/contact/).
+[reach out](https://www.ory.sh/contact/).
 
 Supported CAPTCHA providers are:
 
 - [Cloudflare Turnstile](https://developers.cloudflare.com/turnstile)
 
+Cloudflare Turnstile widgets support a maximum of 10 allowed domains. When CAPTCHA is enabled, this list will be automatically
+populated with your currently configured [custom domains](../../guides/custom-domains.mdx). If your domain list exceeds this
+limit, you won't be able to enable CAPTCHA protection.
+
 ```mdx-code-block
 <Tabs groupId="console-or-api">
 <TabItem value="console" label="Ory Console">