Update availability (cloudflare#23111)

Author: maxvp

src/content/docs/cloudflare-one/policies/gateway/http-policies/file-sandboxing.mdx

@@ -8,7 +8,7 @@ sidebar:
 import { Render, Details } from "~/components";
 
 :::note
-Only available on Enterprise plans. For more information, contact your account team.
+Available as an add-on to Zero Trust Enterprise plans. For more information, contact your account team.
 :::
 
 In addition to [anti-virus (AV) scanning](/cloudflare-one/policies/gateway/http-policies/antivirus-scanning/), Gateway can quarantine previously unseen files downloaded by your users into a sandbox and scan them for malware.