Subdomains: Improve UX to better understand how to set up address resolution for subdomains

[miltonwg]

2 proposals for that in the Subdomains section:

1. Best UX option:
Add a "login with subdomain" button for the user to instantly login with it.
Also add a note explaining: "To set up your subdomain addresses resolution you need to log in with it by pressing this button"

2. Other option:
Add a note to the page where subdomains are shown:
"To set up your subdomain addresses resolution you need to log in with it using the upper right corner 'login' button"

[jessgusclark]

Solution 1 should be doable if the user is the owner of the subdomain.