add example basic program

md/Atari/entries/charset.md

@@ -1,12 +0,0 @@
-<pre class="atari">
-10 GRAPHICS 0
-15 DIM CHAR$(10)
-20 FOR I=0 TO 252
-21 IF I=125 THEN CHAR$="[CLEAR]":GOTO 45
-22 IF I=155 THEN CHAR$="[RETURN]":GOTO 45
-23 IF I=29 THEN CHAR$="[UNPRINTABLE]":GOTO 45
-35 CHAR$=CHR$(I)
-45 PRINT I;" ";CHR$(27);" ";CHAR$
-50 NEXT I
-60 REM USE CONTROL-1 TO PAUSE
-</pre>