documentation update, added STATUS.md document

c64/kernal/plot.s

@@ -1,2 +1,12 @@
+
+;;
+;; Official Kernal routine, described in:
+;;
+;; - [RG64] C64 Programmer's Reference Guide   - page 290
+;; - [CM64] Compute's Mapping the Commodore 64 - page 215
+;;
+;; CPU registers that has to be preserved (see [RG64]): none
+;;
+
 plot:
 	rts