Add multi-repo registry onboarding

README.md

@@ -67,6 +67,13 @@ Feed the running service from this checkout:
 railiance-fabric registry sync --repo-slug railiance-fabric .
 ```
 
+Or register and sync the known local Railiance ecosystem repos from the
+onboarding manifest:
+
+```bash
+railiance-fabric registry sync-manifest registry/railiance-repos.yaml
+```
+
 Ingest a CycloneDX SBOM as queryable library inventory:
 
 ```bash
@@ -81,3 +88,6 @@ GET /repositories/{repo_slug}/snapshots
 GET /repositories/{repo_slug}/snapshots/diff
 GET /search?q=jsonschema
 ```
+
+See `docs/registry-onboarding.md` for the multi-repo manifest and operating
+loop.