Add prereq section

Author: maxvp

src/content/docs/cloudflare-one/policies/gateway/egress-policies/index.mdx

@@ -178,6 +178,8 @@ Gateway uses Rust to evaluate regular expressions. The Rust implementation is sl
 
 ## Limitations
 
+### Selector prerequisites
+
 The [Application](#application), [Content Categories](#content-categories), [Domain](#domain), and [Host](#host) selectors are only available for traffic onboarded to Gateway with [WARP](/cloudflare-one/connections/connect-devices/warp/), [PAC files](/cloudflare-one/connections/connect-devices/agentless/pac-files/), or [Browser Isolation](/cloudflare-one/policies/browser-isolation/). To turn on the selectors for your account, use the [Patch Zero Trust account configuration endpoint](/api/resources/zero_trust/subresources/gateway/subresources/configurations/methods/edit/). For example:
 
 ```sh title="Turn on selectors for egress policies"

src/content/partials/cloudflare-one/gateway/selectors/egress-selector-limitation.mdx

@@ -2,4 +2,4 @@
 {}
 ---
 
-This selector is only available for traffic onboarded to Gateway with WARP, PAC files, or Browser Isolation. For more information, refer to [Limitations](#limitations).
+This selector is only available for traffic onboarded to Gateway with WARP, PAC files, or Browser Isolation. For more information, refer to [Selector prerequisites](/cloudflare-one/policies/gateway/egress-policies/#selector-prerequisites).