Signed-off-by: Pierre Bertet <bonjour@pierrebertet.net>

Adding information about setting multipart/form-data on forms in order
to use file uploads.

Documentation says "Replacing the entire input" but calls Input::merge()
instead of Input::replace().

Signed-off-by: Spencer Deinum <spencerdeinum@gmail.com>

Signed-off-by: Dayle Rees <thepunkfan@gmail.com>