compareprog readme for the exams

subjects/compareprog.en.md

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+## compareprog
+
+### Instructions
+
+Write a program that behaves like the `Compare` function.
+
+This program prints a number comparing two strings lexicographically.
+
+### Expected output :
+
+```console
+student@ubuntu:~/compareprog$ go build
+student@ubuntu:~/compareprog$ ./compareprog a b | cat -e
+-1$
+student@ubuntu:~/compareprog$ ./compareprog a a | cat -e
+0$
+student@ubuntu:~/compareprog$ ./compareprog b a | cat -e
+1$
+student@ubuntu:~/compareprog$ ./compareprog b a d | cat -e
+$
+student@ubuntu:~/compareprog$ ./compareprog | cat -e
+$
+student@ubuntu:~/compareprog$
+```