Add informative comments for future ref

Author: codesungrape

src/main/java/com/codesungrape/hmcts/bookapi/BookApiApplication.java

@@ -11,10 +11,11 @@
 public class BookApiApplication {
 
     /**
-     * Placeholder.
+     * Private constructor to prevent instantiation.
+     * This avoids Checkstyle treating this as an instantiable utility class.
      */
     private BookApiApplication() {
-        // prevents instantiation
+        // Intentionally empty — prevents accidental instantiation
     }
 
     /**