readlink.2: Add free() call to example program

Reported-by: Jonny Grant <jg@jguk.org>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/readlink.2

@@ -320,6 +320,8 @@ main(int argc, char *argv[])
 
     printf("\(aq%s\(aq points to \(aq%s\(aq\\n", argv[1], linkname);
 
+    free(linkname);
+
     exit(EXIT_SUCCESS);
 }
 .fi