Update screen.md

Print should be 'PRINT AT 0, 0; "The character at 9, 10 is "; c$' rather than 'PRINT AT 0, 0; "The character at 10, 10 is "; c$'

Author: spectrumcomputing

docs/screen.md

@@ -28,7 +28,7 @@ SCREEN is a library function to be included with the following command:
 
 PRINT AT 9, 10; "A"
 LET c$ = SCREEN$(9, 10)
-PRINT AT 0, 0; "The character at 10, 10 is "; c$
+PRINT AT 0, 0; "The character at 9, 10 is "; c$
 ```
 
 ##Remarks