Update error message for FindByContactCommand

Make the error message more appropriate for contact numbers

src/main/java/seedu/address/logic/commands/FindByContactCommand.java

@@ -11,7 +11,7 @@ public class FindByContactCommand extends AbstractFindCommand {
     public static final String MESSAGE_USAGE = COMMAND_WORD + ": Finds all persons whose contact numbers "
             + "contain any of the specified keywords (case-insensitive) and displays them as a list with indices.\n"
             + "Parameters: KEYWORD [MORE_KEYWORDS]...\n"
-            + "Example: " + COMMAND_WORD + " alice bob charlie";
+            + "Example: " + COMMAND_WORD + " 91112345 999 995";
     public FindByContactCommand(ContactContainsKeywordsPredicate predicate) {
         super(predicate);
     }