All you need to do is install gedit (suspect nano would have done the job) and type the exact same information I provided to you in that second image. This then creates an icon on the desktop that you have to give it 'trusted' status. I then changed the 'notepad' like icon for the power one and then simply dragged it to the plank - I left the original on the desktop.
You can now sing along to this:http://www.popularyoutube.com/video/_BR ... The-power/
Here's that script 'how-to' in a more readable format:
sudo apt install gedit
After installing gedit and whilst still in Terminal enter:
now copy and paste the code below by clicking on 'Select All' - this copies all of the code to your clipboard for pasting into the new gedit txt file:
Exec=shutdown -Ph now
It will create a 'txt' icon on your desktop and when selecting it it asks if you want to trust it - of course you do!
Right-clicking the icon, select properties and choose the icon of your choice - forgotten where I got mine from and then I just dragged it to the plank.