Added example code

src/example/str_out.asm

@@ -0,0 +1,10 @@
+10;output a string into the top left of the screen
+20        ORG   0100H       ;Start at addr 0x100
+30START:  LD    HL,DATA     ;Load the start address of the string
+40        LD    B,0DH       ;The length of the string (max 255 chars)
+50        LD    DE,0H       ;Start in the top left corner (D=0-3 -> row; E=0-23 column)
+60        CALL  84CDH       ;Call the str_out function in ROM
+70        RET               ;Return from call
+80DATA:   DB    'HELLO, WORLD!'
+90        END               ;End marker for the assembler
+