bug#31584: 27.0.50; Document again what match re-search-backward finds

[Drew Adams]

> It is greedy:
> (with-temp-buffer
>   (insert "xxxxyyyy")
>   (and (re-search-backward "x+y*" nil t) (match-string 0))) ;=> "xyyyy"
> 
> Non-greedy wouldn't match any "y"s.  It's a bit tricky to explain both
> correctly and clearly...

Maybe it would help to say that the pattern is always matched in a forward 
direction, even when it matches text that is before point.

The pattern itself is not read backward (you don't write +x*y
for the reverse search of x+y*), and it doesn't match backward.