Execute user input in ScriptBlock

So I am trying to get [1] this code to work. What I would like is to have is a script that, when run, asks for a command. I would enter the command I want run on the computers I specify, and the script would execute that command on computers in a remote session.

Right now, I either get an error (varies) or no error (but the code doesn't run). Here are the iterations of the specific line I have tried (with "$cmd" being the command to execute):

Invoke-Command -Session $session -ScriptBlock {$cmd}

Invoke-Command -Session $session -ScriptBlock {invoke-expression $cmd}   

Invoke-Command -Session $session -ScriptBlock {$args[0]} -ArgumentList $cmd

I have also tried creating a ScriptBlock before hand using different commands, but no combination has worked. So far for all my searching I have yet to find someone discuss passing user input into "Invoke-Command." Everyone seems to only pass pre-defined commands, which I have no problems running.

Here is the code I am using:

#Get Credentials
$name = [System.Security.Principal.WindowsIdentity]::GetCurrent().Name
$cred = Get-Credential $name

#Get Computer(s)
$comp = read-host "Enter the computer name you would like to run commands on"

#Open Session with specified computer(s)
$session = New-PSSession -ComputerName $comp -Credential $cred

#Execute remote command
$cmd = read-host "Enter the command string to run"
Invoke-Command -Session $session -ScriptBlock {$cmd}

#Close Session
Remove-PSSession $session

In this instance I am trying to run the command "slmgr.vbs /ato" on the remote machine. I know that the command itself works when initiated manually. Do I need to escape the "/"? Also I have tried to use parameters and creating the ScriptBlock separately, but none of these things have worked. Thanks in advance.