includelet's aren't package instances, they're UI snippets that map an include script to a package instance such as forums. You manage them through the layout-managed-subsite admin pages.
Have you created a layout-managed-subsite instance, yet?
Or, if you want your root (/) subsite to be a layout-managed-subsite, have you gone to the admin page and converted that acs-subsite to a layout managed one?
In either case, once you have an unconfigured layout-managed-subsite instance created, visiting the subsite will redirect you to the configuration wizard (you must be admin to do this).
That will step you through various things, among them a page that lists applications and links to a page that allows you to create includelet instance mapped to the app (forums-includelet mapped to forums, etc).
This management/admin page replaces the .lrn applet stuff, which I chose to not re-implement.
Then you'll enter a page configuration page - it's very similar to the .LRN one.
There is some package documentation for layout-managed-subsite, though it's a bit sketchy. Go to your [host]/doc directory and you should see a link there.
Actually I'd love it if you'd look at that documentation and point out what's not clear since obviously, since I wrote the package, the documentation seems crystal clear to me since I already know how the package works!
