implement tasks based on README

src/CourseRegistrationStarter/RegistrationSystem.java

@@ -9,16 +9,25 @@ public class RegistrationSystem {
     }
 
     public void addCourseToSystem(Course c) {
+        this.courses.add(c);
         // TODO: Add the course to the system
     }
 
     public Course findCourseByCode(String code) {
+        for (Course c: this.courses) {
+            if (c.getCourseCode().equals(code)) {
+                return c;
+            }
+        }
         // TODO: Search for a course by course code
         // Return the matching course if found, otherwise return null
         return null;
     }
 
     public void showAllCourses() {
+        for(Course c: this.courses) {
+            System.out.println(c.getCourseName() + ", code: " + c.getCourseCode());
+        }
         // TODO: Print all courses in the system
     }
 }