updated readme.md file

Author: NirmalSilwal

README.md

@@ -2,6 +2,8 @@
 
 Simple calculator for basic math operation developed using Java, AWT, Swing.
 
-### Main_Calculator.java  is the file containing main method.
+**Main_Calculator.java**  is the file containing main method.
 
-### Calculator.java has all the logic for calculator that uses AWT and Swing for the implementation.
+**Calculator.java** has all the logic for calculator that uses AWT and Swing for the implementation.
+
+**My_Calculator.jar** is the executable file, you can use it without any instruction as it is simple calculator.