then open your Cmd on your Pc while connecting your nexus 5 in the bootloader , be sure that you have the correct drivers .
Now navigate to where your recovery was downloaded to . type in
fastboot flash recovery recovery.img
now just go to your TWRP recovery and flash the zip file i attached , that is it you are rooted ! and you are ready to go . some root apps will not work because they are not compatable yet to root in android L.