doc: Extend musttail attribute docs

doc: Extend musttail attribute docs

On Wed, Apr 02, 2025 at 10:32:20AM +0200, Richard Biener wrote:
> I wonder if we can amend the documentation to suggest to end lifetime
> of variables explicitly by proper scoping?

In the -Wmaybe-musttail-local-addr attribute description I've already
tried to show that in the example, but if you think something like
the following would make it clearer.

2025-04-02  Jakub Jelinek  <jakub@redhat.com>

	* doc/extend.texi (musttail statement attribute): Hint how
	to avoid -Wmaybe-musttail-local-addr warnings.