[PATCH] Document how to use --reference

[Andi Kleen]

On Sun, Jan 12, 2020 at 08:51:28PM +0100, Andreas Schwab wrote:
> On Jan 12 2020, Andi Kleen wrote:
> 
> > By popular demand, I did some updates to the git documentation how
> > to use --reference to save disk space.
> 
> I would advice against using --reference.  Nowadays, git worktree is a
> much safer option.

Feel free to do further edits. The file probably needs further work
anyways.

-Andi