Include Sinatra specific instructions. (#211)
Include Sinatra specific instructions. (#211)

Sinatra (starts itself)[https://github.com/sinatra/sinatra/blob/master/lib/sinatra/main.rb#L26] up in an `at_exit()` handler.  Ruby runs multiple `at_exit()` handlers in reverse order of registration.  Sucker Punch does clean up and shutdown in an `at_exit()` handler.  Hence, if SuckerPunch is required *after* Sinatra, Sucker Punch will shut itself down just prior to Sinatra starting up.  

This is a bit surprising; so mention it in the docs.
brandonhilkert/sucker_punch