Improve "Your website is not yet synchronized with your subscription" message.

[WordPresseur]

The message "Your website is not yet synchronized with your subscription. Please add your website from your RocketCDN account page" can be confusing when the domain is already set up in RocketCDN account and when it’s the communication between the site and RocketCDN server which is blocked.

Maybe we could add this:
"146.59.251.59 and https://rocketcdn.me/api/ are probably also blocked by your server, a firewall, or a security plugin. Please allow these on all security levels."