message: Add docs about multiple bindings on same trigger
diff: # binding with the same triggers is defined. To unset a default binding, it can
  # be mapped to the `ReceiveChar` action. Alternatively, you can use `None` for
  # a no-op if you do not wish to receive input characters for that binding.
  +#
  +# If the same trigger is assigned to multiple actions, all of them are executed
  +# at once.
  #key_bindings:
  # (Windows, Linux, and BSD only)
  #- { key: V, mods: Control|Shift, action: Paste }
  