docs/ipc: "urgent": complete the list of container types (#2967)
docs/ipc: "urgent": complete the list of container types (#2967)

Thanks chressie!
stapelberg/i3,Airblader/i3-original,stapelberg/i3,stapelberg/i3,cornerman/i3,Airblader/i3,cornerman/i3,Airblader/i3-original,Airblader/i3,Airblader/i3-original,Airblader/i3,i3/i3,Airblader/i3-original,cornerman/i3,cornerman/i3,i3/i3,i3/i3,Airblader/i3,stapelberg/i3,Airblader/i3-original,i3/i3