Add date to release notes.

RELEASE-NOTES.md

@@ -1,7 +1,7 @@
 ZeroTier Release Notes
 ======
 
-## XXXX-XX-XX -- Version 1.16.1
+## 2025-12-22 -- Version 1.16.1
 
   * Metrics collection is now disabled by default. It can be enabled via the `enableMetrics` setting in `local.conf`.
   * Fix for an issue where metrics were not being recorded while running in daemon mode.