add sample input and sample output in the README.md

Author: dbc2201

.idea/workspace.xml

@@ -6,4 +6,16 @@
 
 ### Problem Statement
 
-Write a program that counts duplicate characters from a given `String`.
+Write a program that counts duplicate characters from a given `String`.
+
+### Sample Input 1
+
+```
+"aabcc"
+```
+
+### Sample Output 2
+
+```
+{a=2, b=1, c=2}
+```