Update to Comments

Updated comments to follow Coding standards to ensure it is easy to read for others.

src/main/java/area/DukeException.java

@@ -1,6 +1,6 @@
 package area;
 /**
- * checks for exception for each command.
+ * Checks for exception for each command.
  */
 public class DukeException extends Exception {
 

src/main/java/area/Todo.java

@@ -1,5 +1,8 @@
 package area;
 
+/**
+ * Todo class is child of Task class. It is used to create objects that represent generic tasks that users want to keep track of.
+ */
 public class Todo extends Task {
 
     /**

src/main/java/area/Ui.java

@@ -1,6 +1,10 @@
 package area;
 import java.util.ArrayList;
 
+/**
+ *  Returns responses to user instructions in the form of printed statements. It starts with greeting the user and ends with the command bye. If any task is added or modified,
+ * Ui will print a statement accordingly to inform user that user's instructions have been followed.
+ */
 public class Ui {
 
     public Ui() {