cmd: document Rosa OS programs

The earlyinit and mbf program are not covered by the compatibility promise, so specify that here.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/earlyinit/main.go

@@ -1,3 +1,7 @@
+// The earlyinit is part of the Rosa OS initramfs and serves as the system init.
+//
+// This program is an internal detail of Rosa OS and is not usable on its own.
+// It is not covered by the compatibility promise.
 package main
 
 import (