Docs should mention that there is no configuration or settings panel

[danyork]

I realized as I was getting ready to tell someone about this plugin that the documentation doesn't say anything about the fact that the plugin "just works". There is no configuration interface, no settings panel, nothing. Updates just appear in the Themes panel when there are updates to display. A note to that effect should be in the docs.

(And as with issue #13 I'll volunteer to add some text if no one else does it first.)

[conover]

Updated the README