Basic 802.11s batman mesh tutorial

I've had success using OpenWRT to create a home network using 802.11s mesh with batman-adv. Big shout-out to @onemarcfifty for his work getting batman-adv supported in the LuCI web interface and his excellent OpenWRT batman tutorial on YouTube! I've created a companion OpenWRT batman tutorial on GitHub. I hope someone finds it useful! Feedback is welcome.