fix(hotkeys: tmux): don't show tmux hotkeys if no rule was specified by user

lib/awful/hotkeys_popup/keys/tmux.lua

@@ -14,10 +14,10 @@ local tmux = {}
 --
 -- For example:
 --
---     tmux.add_rules_for_terminal({ rule = { name = { "tmux" }}})
+--     tmux.add_rules_for_terminal({ rule = { name = "tmux" }})
 --
 -- will show tmux hotkeys for any window that has 'tmux' in its title.
--- If no rules are provided then tmux hotkeys will be shown always!
+-- If no rules are provided then tmux hotkeys won't be shown.
 -- @function add_rules_for_terminal
 -- @see awful.rules.rules
 -- @tparam table rule Rules to match a window containing a tmux session.
@@ -32,6 +32,9 @@ function tmux.add_rules_for_terminal(rule)
     end
 end
 
+-- don't show hotkeys by default
+tmux.add_rules_for_terminal({rule={focusable=false}})
+
 local tmux_keys = {
     ["tmux: sessions"] = {{
         modifiers = {},