Using themekey_ui on node edit forms

I've been monkeying around with the themekey_ui module, which is great. It could benefit from a little documentation in README.txt, though. In particular:

- Admins should go to admin/settings/themekey/settings/ui to make theme options available in node edit forms, and check off the content types they want to enable the options for
- Admins should go to /admin/settings/themekey/settings and enable the node:id property
- Themekey settings are only available on edit forms, not add forms, because they depend on $form->['#node']->nid being set, which won't be the case on add forms. (It would help to relabel the checkbox on admin/settings/themekey/settings/ui as "Show theme option in edit node forms" so admins won't think settings are available on add forms.)

Obviously this is fairly minor, but it would help future users understand how the node editing theme settings work. Thanks!