code: @Nonnull
      public BugInstance addClass(String className, String sourceFileName) {
          ClassAnnotation classAnnotation = new ClassAnnotation(className, sourceFileName);
          add(classAnnotation);
          return this;
      }
docs: Add a class annotation. If this is the first class annotation added, it
  becomes the primary class annotation.
  
  @param className
  the name of the class
  @param sourceFileName
  the source file of the class
  @return this object