docs/ipc: Fix grammar
docs/ipc: Fix grammar

Add missing "it". Also add two instances of "a", which sounds more
correct to me.

Airblader/i3-original,Airblader/i3-original,i3/i3,i3/i3,i3/i3,Airblader/i3-original,stapelberg/i3,i3/i3,Airblader/i3,Airblader/i3,Airblader/i3-original,Airblader/i3,stapelberg/i3,stapelberg/i3,Airblader/i3-original,stapelberg/i3,Airblader/i3