license: Add Frédéric to RELICENSE.md

I, Frédéric Danis, agree to relicense my contributions to NetworkManager as LGPL-2.1+ as proposed by Thomas Haller.

Some of my work may be held under copyright by Sigfox or Collabora Ltd. I do not speak for those entities.

Signed-off-by: Frédéric Danis frederic.danis.oss@gmail.com