Respond with a help message if command is not recognized

[tk3369]

If you typed a command that isn't recognized then it should display a help message. For example:

,tz

I just reviewed the code again. There should be an easy fix around here:

HoJBot.jl/src/command/tz.jl

Lines 13 to 16 in 9ef4950

	function time_zone_commander(c::Client, m::Message)
	# @info "time_zone_commander called"
	# @info "Message content" m.content m.author.username m.author.discriminator
	startswith(m.content, COMMAND_PREFIX * "tz ") || return