Correct location of settings.cfg

When I added information about `settings.cfg` and an example version in
20a0de5, I added `instance` in the wrong location. It belongs in the top
level directory, not inside the application's package.

Fixes #40
Merge pull request #41 from NYCPython/fix-settings-in-readme

Correct location of settings.cfg
Merge remote-tracking branch 'origin/master'