Include insert-user binary in the Debian package

[Kyle Maas]

Considering you need the insert-user program to actually start using go-ssb-room, it would be nice if a compiled version of that was included in the Debian package.

[decentral1se]

Was underway in #266 but needs picking up again...

This is a dupe of #241?

[Kyle Maas]

Yep, I'd say so.