[Workers] Add custom-domain limits to routing section (#17939)

Author: taylorlee

src/content/docs/workers/platform/limits.mdx

@@ -282,11 +282,17 @@ If you need more than 500 Workers, consider using [Workers for Platforms](/cloud
 
 ---
 
-## Number of routes per zone
+## Routes and domains
+
+### Number of routes per zone
 
 Each zone has a limit of 1,000 [routes](/workers/configuration/routing/routes/). If you require more than 1,000 routes on your zone, consider using [Workers for Platforms](/cloudflare-for-platforms/workers-for-platforms/) or request an increase to this limit.
 
-## Number of routed zones per Worker
+### Number of custom domains per zone
+
+Each zone has a limit of 100 [custom domains](/workers/configuration/routing/custom-domains/). If you require more than 100 custom domains on your zone, consider using a wildcard [route](/workers/configuration/routing/routes/) or request an increase to this limit.
+
+### Number of routed zones per Worker
 
 When configuring [routing](/workers/configuration/routing/), the maximum number of zones that can be referenced by a Worker is 1,000. If you require more than 1,000 zones on your Worker, consider using [Workers for Platforms](/cloudflare-for-platforms/workers-for-platforms/) or request an increase to this limit.