docs: update release notes for local file embedding feature

Resolves #179

Author: Okeanos

docs/release-notes.md

@@ -13,6 +13,7 @@ nav_order: 9
 
 - Add RHEL for Edge (`r4e`) spec 1.0.0 and 1.1.0-experimental, targeting
   Ignition spec 3.3.0 and 3.4.0-experimental respectively
+- Support local file embedding for SSH keys and systemd units
 
 ### Bug fixes