Add page on robotics prelim

[a-nooj]

Create a post on guidelines for the robotics prelim exam -- similar to Mozer's page.

Incorporate Alessandro's message from Slack --

Rough plan for prelim is :

1. you publish / submit a couple papers
2. you get a sense of what you are interested in doing as a grown up (i.e. after the prelim)
3. you write a survey paper on the topic of interest (which may be published afterwards)
4. you present your survey paper to the commitee alongside a brief plan of work