How to add www subdomain

I bought a domain from namecheap.com and set up my domain (conceptgrapher.org) for a droplet running ubuntu 12.04.

I have an nginx server listening on port 80 in the droplet. I’m now able to access conceptgrapher.org from the browser, but I also want to access www.conceptgrapher.org

After some googling I found http://support.godaddy.com/groups/dns-management-and-services/forum/topic/adding-www-to-my-domain-name/

According to my understanding I need to add a CNAME record. So I added a CNAME from the DNS tab in the cloud.digitalocean.com console: Enter Name: www Enter hostname: conceptgrapher.org. (with a ‘.’ in the end)

I’ve attached a screenshot of the values I entered too: http://imgur.com/1REv6rO

But www.conceptgrapher.org remains unresolved: $ nslookup www.conceptgrapher.org Server: 127.0.0.1 Address: 127.0.0.1#53

** server can’t find www.conceptgrapher.org: NXDOMAIN

But just conceptgrapher.org works fine $ nslookup conceptgrapher.org Server: 127.0.0.1 Address: 127.0.0.1#53

Non-authoritative answer: Name: conceptgrapher.org Address: 146.185.175.174

How to resolve the issue? Thanks!