Update usage instructions

[dvisockas]

I just added a cd rivalctl so that it can be copied from the repo and pasted into a terminal. In a current scenario, when a person pulls a repository, he is in some directory, not in rivalctl, thus sudo python setup.py install fails because probably in that directory there is no setup.py file.

Maybe it would be better to still keep in two lines, just edit the second line to be sudo python rivalctl/setup.py install :grey_question:

:heart: :fireworks: