Clarify speech mode (#16069)
Summary of the issue:
Everyone may not know what speech modes are, especially the new on-demand mode.
Description of user facing changes
In the User Guide, there is a paragraph describing the setting to change available speech mode in the cycling command. A link has been added to the paragraph describing the speech modes.
While at it, I have also rephrased a script's documentation, which inappropriately mentions "peech modes" when referring to language switching possible values; this way, it's not confusing anymore when searching for "speech mode" in the UG
