Please mention `which -a` in the docs

[rrthomas]

I can't find a where utility for GNU/Linux, nor indeed more generally any trace of such a thing (admittedly difficult to search for!). However, which -a seems to do much the same, so maybe you could mention that in the documentation for users who might be interested?

[plicease]

Done.

[rrthomas]

Thanks very much for this prompt fix.