awesomerc: Add comment mentioning c.requests_no_titlebar

Signed-off-by: Uli Schlachter <psychon@znc.in>

awesomerc.lua

@@ -521,6 +521,10 @@ awful.rules.rules = {
     -- @DOC_DIALOG_RULE@
     -- Add titlebars to normal clients and dialogs
     { rule_any = {type = { "normal", "dialog" }
+      -- If you want programs to be able to request no titlebars, use:
+      -- For client side decorations, clients might request no titlebars via
+      -- Motif WM hints. To honor these hints, use:
+      -- titlebars_enabled = function(c) return c.requests_no_titlebar end
       }, properties = { titlebars_enabled = true }
     },