Write a Makefile and a script for automatic instance deployment #5

Carried over from TODO.md. Add a Makefile for the build (embed tag, ldflags, version stamp) and a script that deploys an instance.

The Makefile landed in !22 (issue #34): build, test, lint, dist, plus binaries attached to releases. A deployment script was not written; the systemd unit and README run section from !18 cover installing an instance by hand. Reopen if a script is still wanted.