Update virtual-network-workspaces-resources.md

Author: dlepow

articles/api-management/virtual-network-workspaces-resources.md

@@ -27,7 +27,7 @@ For information about networking options in API Management, see [Use a virtual n
 
 * The virtual network must be in the same region and Azure subscription as the API Management instance.
 
-## Subnet size
+## Subnet requirements
 
 * The subnet can't be shared with another Azure resource, including another workspace gateway.