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.
Add tip about the message at the root path
Merge pull request #112 from maxlinc/patch-1

Add a Quick start section to the README