added ram disk status message on startup screen

src/dos_m65/dos_rdchk.s

@@ -0,0 +1,24 @@
+
+;
+; Preload RAM disk image
+;
+
+
+dos_RDCHK:
+
+	; Before the start make sure memory content is not damaged
+
+	jsr dos_MEMCHK
+	bcc @ok
+	lda #$FF
+	jmp dos_EXIT_SEC_A
+
+@ok:
+	jsr dos_ENTER
+
+	lda RD_MSG              
+
+	ldx #$FF                 ; reset the message after it gets displayed
+	stx RD_MSG
+
+	jmp dos_EXIT_CLC_A