Add a Quick start section to the README

I can never remember what value I'm supposed to use for the endpoint when I want to use Mimic. Having a curl and OpenStack CLI example shows the proper value for OS_AUTH_URL settings and how to see the service catalog to get a list of other product-specific endpoints.
I feel like the logs might not be the right to place to put them. I would like it to be in a readthedocs or a wiki page. Mind creating an issue for this, so we can discuss this further and resolve it.