refactoring: description added

src/convert_M_in_KM.c

@@ -1,7 +1,7 @@
 
 #include "convert_M_in_KM.h"
 #include <stdio.h>
-//convert length
+//convert length for double
 double meter_to_kilometer(double meter) {
     return meter / 1000.0;
 }