** This is the super chopped down version that worked between my Ubuntu laptop and my Arch Rasp ** This isn't peristent after reboot, but it works for now :)
Step zero: plug everything in.
Step one, on the laptop:
sudo ip addr add 192.168.1.1/24 dev eth0
Step two, again on the laptop:
sudo iptables -A FORWARD -o wlan0 -i eth0 -s 192.168.1.0/24 -m conntrack --ctstate NEW -j ACCEPT
sudo iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
sudo iptables -A POSTROUTING -t nat -j MASQUERADE
Step three: enable IP forwarding, again on the laptop.
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward
Step four: sudo ifconfig eth0 up on the laptop makes sure it's listening for packets.
Step five: on the Pi, get an IP address.
sudo ip addr add 192.168.1.2/24 dev eth0
Step six: again on the Pi, tell it where to find the internet
sudo ip route add default via 192.168.1.1
Step seven: to get DNS working, I ignored what the Ubuntu wiki was saying about dhcp. Just edit /etc/resolv.conf and add the line
nameserver 89.233.43.71 89.104.194.142