exam exercise readme for alphamirror

subjects/alphamirror.md

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+# alphamirror
+## Instructions
+
+Write a program called alpha_mirror that takes a string and displays this string
+after replacing each alphabetical character by the opposite alphabetical
+character, followed by a newline.
+
+'a' becomes 'z', 'Z' becomes 'A'
+'d' becomes 'w', 'M' becomes 'N'
+
+and so on.
+
+Case is not changed.
+
+If the number of arguments is not 1, display only a newline.
+
+And its output :
+
+```console
+student@ubuntu:~/student/alphamirror$ go build
+student@ubuntu:~/student/alphamirror$ ./alphamirror "abc"
+zyx
+student@ubuntu:~/student/alphamirror$ ./alphamirror "My horse is Amazing." | cat -e
+Nb slihv rh Znzarmt.$
+student@ubuntu:~/student/alphamirror$ ./alphamirror | cat -e
+$
+student@ubuntu:~/student/alphamirror$ 
+```