Some unnamed corporate lawyers twitchy about the GPLv3 have expressed
concern that the *output* produced by Flent would somehow be affected by
the source code license. This is of course preposterous; however, rather
than take on the Sisyphean task of arguing the absurdity of that claim,
let's add an explicit clarification to the documentation and the license
file.

Whether this will actually help convince everyone is of course debatable,
but who knows? Stranger things have certainly happened...

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>