[RFA 01/12] Fix help and documentation for inferior commands

[Eli Zaretskii]

> From: Tom Tromey <tom@tromey.com>
> Cc: Tom Tromey <tom@tromey.com>
> Date: Mon, 30 Apr 2018 08:37:20 -0600
> 
> While doing this I noticed that the manual doesn't document the
> argument to "info inferiors", so I've added that as well.

Thanks.

>  @table @code
> -@kindex info inferiors
> +@kindex info inferiors [ @var{ID}@dots{} ]

"ID" should be in lower-case.  (It will be rendered in caps in Info,
but not in the printed output, where it will be typeset in the slant
typeface.)

> +By default all inferiors are printed, but an argument can be used to
> +limit the display to just the requested inferiors.

This should reference @var{id} and explain what the "id" there is.
Someone might think it's a PID, for example.