CONTRIBUTING.md explains the fork relationship, branch model, generated-
code workflow, and what changes we will and won't accept (no re-enabling
Solana/Tron/Zano/Decred/Zcash, no Cake-domain endpoints, no Lightning
yet, no telemetry).
README.md: removed the stale ./scripts/prepare_zcash.sh reference (file
doesn't exist) and added a link to CONTRIBUTING.
.gitignore: untrack docs/UPSTREAM_SYNC.md (internal merge-strategy
playbook, kept locally alongside docs/links.md).
