[chirp_users] PPA for Ubuntu 16.10 (Yakkety)

Chirp seems to update correctly under Ubuntu 16.10 provided that the repository used is the same as that for Xenial.

For completeness, might it be possible to copy the Xenial PPA as the Yakkety version so that adding the repository under Yakkety does not generate an error when attempting a software update?

David, 2E0FNY