Ask HN: Recommended reads for an electronics beginner?

I've seen the influx of small single board computers (e.g. Raspberry Pi, Vocore, Orange Pi) and have a bunch of ideas for projects for these that I'd like to try. But the majority require some modifications to the board.

For example, I'd want to add a second ethernet port to the Vocore2, but I know it's not as simple as soldering an ethernet port to the appropriate pins on the SOC (e.g. some magnetics are required). Ultimately I'd like to be able to design my own board.

I've got a strong CS, Linux, networking background, and understand the basics of electronics, but don't know where to begin when it comes to electrical engineering.

Any book/tutorial recommendations or advice gratefully received!