You're right, the documentation you've found isn't particularly useful. Right now it's written for plugin developers, and technically speaking content type plugins don't quite follow that process either. We tried to make this easier and install both of these plugins by default on V2. You can check to see if they are installed by by looking in your Gemfile.lock and making sure there are entries for "concerto_simple_rss" and "concerto_remote_video".
If you're not seeing the option to create those two content types when you are on /content/new it might be because you don't have any feeds that allow that content type. In V2 we introduced the ability to control what content types can be submitted to a feed, there are check boxes on the feed edit page which will control this. I would visit /feeds/<id>/edit (or click the edit button next to a feed on the v2 homepage) and make sure all the content type checkboxes are checked, including the video and rss ones. Even if they are all checked by default, click "save" to force that setting to stick... we've had a bug or two where the UI shows them as checked and the backend does not.
Let me know how it goes!
Thanks,
~Brian M