jshell tool: missing references in /help /set mode

Reported by Joni Gordon:
"the online help for /set mode mentions <new-mode> but that isn't in the help anywhere:
jshell> /help /set mode
| Create a user-defined feedback mode, optionally copying from an existing mode:
|
| /set mode <mode> [<old-mode>] [-command|-quiet|-delete]
| Retain a user-defined feedback mode for future sessions:
|
| /set mode -retain <mode>
|
| Delete a user-defined feedback mode:
|
| /set mode -delete [-retain] <mode>
|
| Show feedback mode settings:
|
| /set mode [<mode>]
|
| Where <new-mode> is the name of a mode you wish to create.
| Where <old-mode> is the name of a previously defined feedback mode.

"