Calling a PowerShell script to prompt for $servername or text file

I have this script working on 2008 R2 servers when run remotely with domain admin user: It creates a local user and then adds that user to local Administrators account.

$cn = [ADSI]"WinNT://$servername.com"

$user = $cn.Create("User","_decommission")

$user.SetPassword("P@ssword1")

$user.setinfo()

$user.Description = "Test user"

Invoke-command -computername $servername.com -scriptblock {net localgroup Administrators /add $servername\_decom}

How do I utilize vCO to call this script to where I have it prompt me for the $servername and/or to point to a text file with the list of servers??

Please help..