Update USERS.md
Update USERS.md

Added Nexxiot to the list of Cilium users.

Signed-off-by: Alex Berger <8ca52447ae9ba0eb8b3f3b64bd9706b328eb129d@gmx.ch>
cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium