Revise README

[paulsonnentag]

I would like to change a few things about the readme:

• make the feature list more descriptive, there seems to be be some duplicates
• remove 'use chrome' instruction. I think robotopia should work in all browsers, if that's not the case we should fix that

Thoughts?

[paulsonnentag]

Talk is cheap, so I'm going to make robotopia run in most current browsers #122

[stritti]

Added also some more instructions for local installation in PR: #137