change to howtos:hardware:arm:raspberrypi3_network

Hi bifferos, I added instructions to avoid saving the installer host key in the first place to your howto. Please review the changes.

https://docs.slackware.com/howtos:hardware:arm:raspberrypi3_network?do=diff&rev2%5B0%5D=1535327742&rev2%5B1%5D=1710153198&difftype=sidebyside