Improve module usability

As part of my preparation for a usability presentation reviewed you module. The module itself serves a usability purpose for site builders and admin, thank you for this.
I have a few usability quick wins for the module:

* Add a README.txt file containing basic module and installation information.
* Implement hook_help(). A module help page automatically lists (with links) the available administration pages (permission, settings)
* Move the Settings page (currently under Content Management) to Site configuration. Although the module is content related, it is common use to have module settings available under Site configuration.
See also: #161085: Module documentation guidelines