Change reason for waiting

Apparently one has to wait, but DNS can't be involved at this step. (As the DNS records had already to be ready and presumably propagated for the ACME challenge to work.) So let's assume it's the content delivery network serving the certificate that needs some time here.

doc/user/project/pages/lets_encrypt_for_gitlab_pages.md

@@ -141,7 +141,7 @@ Now that your certificate has been issued, let's add it to your Pages site:
     ```
 
 1. Click **Save changes** to apply them to your website.
-1. Wait a few minutes for DNS propagation.
+1. Wait a few minutes for the configuration changes to take effect.
 1. Visit your website at `https://example.com`.
 
 To force `https` connections on your site, navigate to your