I've done just this.
I actually created a separate folder in my Plex TV Shows library (so that collection in Plex points to multiple folders), and moved media over to that folder for the shows that I want Channels to import and know about. Then added the folder to the Local Content place in the DVR Settings, and refreshed.
Some gotchas are in the indexing. Channels relies on the subdirectory being the name of the series, so you can't just point it at a mass of video files, or even directly to a folder with Season_XX subfolders. It also doesn't appear to deal well with underscores in lieu of spaces in the show name, so "Night_Court" wasn't detect properly, and ended up in the unmatched place tmm1 pointed you to.
Once that happened, I setup a collection and added the TV shows I wanted for the virtual channel into the collection. You can also use a smart rule there, rather than manually adding content. I then added that collection to the virtual channel. This way I can just add more content to that collection when I want to. You can wait for it to reindex, or you can force it to refresh the guide data for your virtual channel, and your new content should start.