Add quick start instructions

[chapulina]

Addresses issue #2

[jubeira]

These were the steps I had followed on my own when I read the slides and the resources, so I'd say it's the way to go. The problem is that I still couldn't see the robot model in the browser. Any ideas?

[jubeira]

Alright, for the record:

• My issue was rosbridge_webserver. The robot didn't show up because roslibjs wasn't retrieving rosparams correctly, just as described in this question.
• I tried the most basic roslibjs tutorial, and I apparently rosbridge wasn't sending messages both ways: web --> ros was alright, but ros --> web was not (i.e. basically the only thing that worked was publishing messages).
• After some research I ended up in this comment. I reinstalled twisted and roslibjs started working properly.

I'll add the conclusions to a troubleshooting section.

[jubeira]

Done @chapulina; PTAL. I think we can get this merged already.