docs: require hardlink-safe route mount topology

docs/deployment-and-usage.md

@@ -128,7 +128,11 @@ advertised_addresses = ["dynamic"]
 When an existing Syncthing folder is physically nested in the qB data root,
 use a `local_path_overrides` entry to map that exact Syncthing API path through
 the same client bind mount. This enables hardlinks without creating two Docker
-mount boundaries for the same host files.
+mount boundaries for the same host files. Do not add a second bind mount for
+the nested folder: Linux treats it as a distinct mount even when it has the
+same `st_dev`, and the client correctly falls back to copy-only capacity
+accounting. See the production deployment README for the required compose and
+override pattern.
 
 The remaining node examples omit optional `[connection]`, `[jobs]`, and
 `[backup]` tables and therefore use these same defaults; deployments may