If all you need is a list of the group members:
Get-ADGroupMember "Remote Desktop Users" -Recursive | Select samaccountname
gives you a list of accounts names, OR
Get-ADGroupMember "Remote Desktop Users" -Recursive | Select name
gives you a list of the user's name (as entered into AD)
Save yourself some time and finish by piping output to a file with something like:
abovecommand | Out-File "C:\Users\username\Desktop\RDU_members.txt" -Append
If you still want to pull the full description of the group itself, you could use:
Get-ADGroup -Filter {name -like "Remote Desktop Users"}
OR you could simply remove the select from one of the first two statements to keep the same format of output (one block per account).
Salt and pepper to taste. Hope this helps.