Restructure the README around what Horizon is, its status, how to build it
from your own copy of the game, and its parity table. The Java performance
pack material and the research lab notes move to docs/java-packs.md and
docs/research-lab.md. The target platform is stated generically instead of
naming a machine, the stale list of missing mobs is dropped in favour of the
audited table, and the legal notice follows Mojang's usage wording.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Ludovic Marie