improve documentation of tcl vs. dcc need-*

[thommey]

.chanset does not include {} for need-* settings, Tcl does, might be confusing. Clarify on https://docs.eggheads.org/coreDocs/channels.html maybe.

Found by: Koragg

[thommey]

Could maybe also warn if it starts with a literal '{'?

[vanosg]

@thommey Can you add some words here and I'll include it with what I'm working on now?

[thommey]

Note: Be aware that the syntax for setting the need- settings is different between Tcl's [channel set] and the dcc .chanset command.
.chanset #chan need-op putmsg NickServ "op #chan"
but
channel set #chan need-op { putmsg NickServ "op #chan" }