Add description of meaning of csv columns

src/main/java/fr/ntr/AccessPoint.java

@@ -58,7 +58,7 @@ public class AccessPoint {
         try{
             Files.deleteIfExists(Paths.get("data.csv"));
             this.outputDataFile = new FileOutputStream("data.csv", true);
-
+            outputDataFile.write("tick;x;y;user;bandwidth;\n".getBytes());
         }catch(IOException e){
             System.err.println("Cannot create the output file");
             System.exit(1);