fix OperationGroup documentation

[iscai-msft]

Right now, if users find the operation they want to call, they find it on an operation group. This makes their first thought be to create an operations group to get this operation. Instead, we want to direct users back to the client, since users should be calling the operation through the client. Figure out a way to have the operation's docstring show up closer to the client itself, so users' first idea is to call them from the client