automatically mount a shared folder in Ubuntu guest

I still cannot get the shared folder to automatically load each time i start Ubuntu
This is a list of the steps i have carried out so far:

1 - I have installed the guest additions
2 - I have specified a folder to share and the name of the folder is "FOLDERS" whick is located on my "K drive" which is an external drive
3 - sudo mkdir /media/windows-share
4 - sudo mount -t vboxsf folders /media/windows-share
5 - gksudo gedit /etc/init.d/rc.local /mount -t vboxsf folders /media/windows-share
6 - ls /media/windows-share (this command listed the contents of the shared folder)
7 - Each time i restart the Ubuntu operating system, the folder would not be mounted unless i have to go through the same process of mounting it again each and everytime. Please, from the description i have given above, could you tell me what i have done wrong and possibly how to make sure that the shared folder is automatically mounted each time i start the Ubuntu guest operating system. I look forward to your response. Thank you