added documentation for OFF

[Svetlana-T]

Credit to KindOne at #libera for mentioning this is not documented

[RealKindOne]

After reviewing the chanserv/set_mlock source code and a bit of testing I have determined that I am wrong on that command.

You only need cs set #channel mlock remove the mlock. Anything invalid like OFF, nonexistent modes, oper-only modes (while not oper), has the same effect and remove the mlock.

There are a few other command's that accept multiple ways to disable them, but they are not documented on how:

ChanServ SET EMAIL
ChanServ SET ENTRYMSG 
ChanServ SET URL

They accept , NONE, and OFF

atheme/modules/chanserv/set_entrymsg.c

Line 40 in ab7319d

if (!parv[1] || !strcasecmp("OFF", parv[1]) || !strcasecmp("NONE", parv[1]))

atheme/modules/chanserv/set_email.c

Line 39 in ab7319d

if (!mail || !strcasecmp(mail, "NONE") || !strcasecmp(mail, "OFF"))

atheme/modules/chanserv/set_url.c

Line 39 in ab7319d

if (!url || !strcasecmp("OFF", url) || !strcasecmp("NONE", url))