bug#34937: [PATCH] update user docs for emacs-gnutls; tofu and program vs built-in

[Noam Postavsky]

Tara Sawyer <tara@anne.cat> writes:
  
> +To debug GnuTLS problems, first check the messages buffer, and then
> +check the function below @code{gnutls-log-level}
> +
> +If GnuTLS is not available as a built-in (@code{gnutls-available-p}
> +returns an empty list (), emacs will call out to the @code{gnutls-cli}
> +program to perform TLS connections.  If you need to modify
> +the command it calls you can do this with the variable
> +@code{tls-program}.
> +For example, if you want to pin a certificate and use Trust On First
> +Use(TOFU), then something like this:
> + @code{(add-to-list 'tls-program "gnutls-cli --tofu --x509cafile %t -p
> + %p %h ")}
> + will probably serve you well.

tls.el is getting obsoleted in Emacs 27 (see Bug#31457), so I don't
think we want to add documentation about it.  Basically, you should only
be using it if you really know what you're doing already.