Instance connect tab should talk about SSH

[david-crespo]

Extremely obvious in hindsight. I suspect most people clicking the connect tab are not looking for the serial console, and are instead looking for SSH or VNC. We should say something about SSH, like

If you specified SSH keys when you created the instance, you can connect to it through an external IP [copy dynamic based on whether it has external IPs]:

ssh username@[actual IP]

Blah blah blah, username depends on the OS, etc.

and ideally link to a doc. The quick start appendix has a section about creating SSH keys — maybe that should be its own guide.

Re: VNC, we don't do a lot of "coming soon" in the console, so we should probably just link to a doc. (We don't have a doc yet.)