Add inject documentation

Co-authored-by: Marwan Sulaiman <marwan.sameer@gmail.com>

Author: lonnywong

session.go

@@ -10,6 +10,7 @@ import (
 // Session represents an iTerm2 Session which is a pane
 // within a Tab where the terminal is active
 type Session interface {
+    Inject injects bytes as input to the terminal, as though the running program had produced them.
 	Inject(b []byte) error
 	SendText(s string) error
 	Activate(selectTab, orderWindowFront bool) error