Create readme.md

Author: syeedameen

src/io/readme.md

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+### INPUT AND OUTPUT DEVICES SUBROUTINES 
+
+
+Description                 |   Code 
+----------------------------|------------------
+seven segment display       |   [sevenseg]
+4x4 Matrix Keypad           |   [keypad]
+
+
+
+[sevenseg]:(https://github.com/syeedameen/mcs-51-subroutines/blob/master/src/io/7seg.asm)
+[keypad]:(https://github.com/syeedameen/mcs-51-subroutines/blob/master/src/io/keypad.asm)