It doesn't support adding highlights from books; I primarily listen to audiobooks these days so it wasn't a feature that made the cut when I was defining the scope for Notado. Additionally I think that Readwise already handles this use case very well.

I would like to support automatically syncing notes from Notado to Readwise, but it seems that they do not provide a public API yet. It's still possible to indirectly synchronise notes from Notado to Readwise by syncing them to Instapaper as Highlights, and then syncing those Highlights to Readwise, though this isn't something I have done myself so I can't vouch for the reliability of it.