Import-Module Tridion-CoreService
Set-TridionCoreServiceSettings -HostName "my-cm-server" -Version Web-8.5 -ConnectionType Basic-SSL -Persist
New-TridionUser -UserName "domain\username" -Description "Person Name" -MakeAdministrator
# For Web 8.5 the -MakeAdministrator option does not work, you have to add the user to the System Administrator group instead
# New-TridionUser -UserName "domain\username" -Description "Person Name" -MemberOf "System Administrator"