Appending the computer description in AD

Hi all,

I'm new here, and not really a scripting person, I use PS scripts that usually have been created for me or I can find online. This one really has me baffled, I'm trying to append the computer description with the following script, but it just keeps over writing it.

Get-ADComputer Joet -Properties Description | Set-ADComputer -Description {$_.Description + "help"}

It over writes the description with everything inside of the brackets.....any help would be appreciated.

Thanks!