If you'd like to host your newsroom on a custom domain including SSL/HTTPS support then you should start by requesting a SSL certificate first.
1. Create a CNAME entry
A CNAME entry is the mapping of a host name on a domain that you own, to another host name of your preference (read more). This operation can be done by anyone who can access your account with the domain name registrar (DNS).
In this case the alias name should be, for example, 'news.yourdomain.com', and the target to points to should be 'cname.pr.co'.
Once you see a pr.co error page appear on news.yourdomain.com your are all set up and you can continue to the next step. Please note that this could take a little while (up to 24 hours).
2. Set the domain for you newsroom
Sign in to your pr.co account, go to the newsroom you'd like to update and click on Settings > General > Use your own domain. Fill-in "press.yourdomain.com" in the "Use your own domain" field.
Click of Save changes and you are all done!