Tell user that nothing was found by grep/that grep is still running

[mimgrund]

When grepping for something, it is not clear when the search has ended thus leaving the user with the need to guess when to exit.

@quchen has found a "nice" workaround: "Wenn ich nach einer Weile nichts finde, gehe ich aus vgrep 'raus und greppe nochmal manuell. Wenn ich dann nichts finde, weiß ich, dass ich nichts finde."

However, I'd prefer a more reasonable builtin solution.

cheers Max