Add quoting for sample command

Long description:

The user's guide talks about renaming workspaces, for example to
"2: mail", and a sample key binding for use with i3-input is supplied.
However, this example lacks proper quoting for the format string, so
that when workspace name with a space in it, like "2: mail", is given,
the current workspace is renamed to "2:". This patch adds proper
quoting.

To apply this patch, use:
curl http://cr.i3wm.org/patch/265/raw.patch | git am

@@ -1590,7 +1590,7 @@ i3-msg 'rename workspace 5 to 6'

 i3-msg 'rename workspace 1 to "1: www"'

 i3-msg 'rename workspace "1: www" to "10: www"'

 i3-msg 'rename workspace to "2: mail"

-bindsym $mod+r exec i3-input -F 'rename workspace to %s' -P 'New name: '

+bindsym $mod+r exec i3-input -F 'rename workspace to "%s"' -P 'New name: '

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 === Moving workspaces to a different screen