d/neopi.1: fix line breaking error

Let's put supported extensions in a list, so man can properly handle the
line breaking.

This solves lintian warning:
 W: neopi: manpage-has-errors-from-man usr/share/man/man1/neopi.1.gz

Signed-off-by: Arturo Borrero Gonzalez <aborrero@cica.es>