message: Fix - yml: mention `showkey -a` to get x sequence from key
  Am not touching the -macos yaml, as I'm not sure this works under macOS.
diff: @@ -158,6 +158,10 @@ visual_bell:
  # specified string every time that binding is activated. These should generally
  # be escape sequences, but they can be configured to send arbitrary strings of
  # bytes. Possible values of `action` include `Paste` and `PasteSelection`.
  +#
  +# Want to add a binding (e.g. "PageUp") but are unsure what the X sequence
  +# (e.g. "\x1b[5~") is? Open another terminal (like xterm) without tmux,
  +# then run `showkey -a` to get the sequence associated to a key combination.
  key_bindings:
  - { key: V, mods: Command, action: Paste }
  - { key: C, mods: Command, action: Copy }
  