documentation update, added STATUS.md document

c64/kernal/unlsn.s

@@ -1,4 +1,14 @@
-; Function defined on pp272-273 of C64 Programmers Reference Guide
+
+;;
+;; Official Kernal routine, described in:
+;;
+;; - [RG64] C64 Programmer's Reference Guide   - page 303
+;; - [CM64] Compute's Mapping the Commodore 64 - page 224
+;;
+;; CPU registers that has to be preserved (see [RG64]): .X, .Y
+;;
+
+;; XXX currently does not preserve registers, to be fixed!
 
 unlsn: