The README opened straight into cargo build, which is the wrong first
instruction for someone standing up a shard: the installer places this
binary, its config, a service account and the service registration.
Adds a short operator section pointing at the installer (and at INSTALL.md
Appendix A3-A4 for installing by hand, still supported), marks everything
below it as development, and lists the installer under related repos.
Co-Authored-By: Claude <noreply@anthropic.com>