serial setup for pi3/4/5

[knickels]

This PR gives instructions for how to connect GPIO 14/15 to /dev/ttyAMA0 which should work for pi3/4, and pi5. It also adds a back in a pointer to serial_config_info.md which got orphaned in a previous PR, and updates a stale URL referencing the roboclaw setup in the main repo. I guess maybe that last one might be a separate PR - lmk if you want me to split them.

[Achllle]

I'm by no means an expert on this stuff, but in #187 I seemed to have found that no config.txt hacking was needed if you configured the rpi-config tool correctly. In my head the serial_config_info.md file was just outdated and isn't in line anymore with the changes from #187
If you're convinced this is the right approach, I'll follow along.

I don't have a RPi5, but my understanding was that there's no miniUART anymore and two fully fledged UARTs which allows running serial and bluetooth at the same time. I think a lot of people would want to use RPi5s because it allows them to use a bluetooth controller.