Clean install on MacOS, needs also a MySQL Installation

[idev]

Hello,

I installed sketchy by following the manual steps on the manual. But it skipped on step "python setup.py install" with the error EnvironmentError: mysql_config not found.

After installing mysql with brew install mysql, everything works fine!

Thanks for your great work.

[sbehrens]

Sketchy prod uses mysql as the recommended database engine. I'll add some guidance in the documentation on that dependency.

[sbehrens]

Wiki updated.