Name the function, which has to be implemented.

hw2/task1/README.md

 
 ## task
 
-Calculate the Hamming difference between two DNA strands.
+Calculate the Hamming difference between two DNA strands by implementing 
+the library function *hamming_distance(s1: &str, s2: &str) -> Result<usize, String>*.
 
 A mutation is simply a mistake that occurs during the creation or
 copying of a nucleic acid, in particular DNA. Because nucleic acids are