bug#48504: Improve style of C-h t description (Preface)

[Eli Zaretskii]

> From: Sebastian Urban <mrsebastianurban@gmail.com>
> Date: Tue, 18 May 2021 21:05:14 +0200
> 
> Currently, in the Preface of the Emacs manual (EMACS.TEXI - L1291),
> there is:
>     To run the tutorial, start Emacs and type @kbd{C-h t} (which is
>     ``control h and then t'').
> 
> I think, the part between parens should look better, e.g. similar to
> this part of SCREEN.TEXI (L126):
>     ...(hold down @key{Ctrl} and type @kbd{x}, then let go of
>     @key{Ctrl} and type @kbd{=})...
> ...i.e.:
>     ...(hold down @key{Ctrl} and type @kbd{h}, then let go of
>     @key{Ctrl} and type @kbd{t}).

We didn't yet introduce the Ctrl etc. notation at that place.