feat(serverless): explain that containers are accessible on ports 80 and 443 from the internet

Author: ahamez

pages/serverless-containers/concepts.mdx

@@ -156,6 +156,10 @@ The value defined in the port parameter will then be passed to your container du
 Only one port can be exposed per Serverless Container.
 </Message>
 
+<Message type="note">
+Your container is accessible from the internet via ports 80 and 443, regardless of the specified port. The value you set determines how the Scaleway infrastructure accesses your container.
+</Message>
+
 ## Privacy policy
 
 A container's privacy policy defines whether a container may be invoked anonymously (**public**) or only via an authentication mechanism provided by the [Scaleway API](https://www.scaleway.com/en/developers/api/serverless-containers/#authentication) (**private**).