Let others know why this code is here

[ci skip]

activemodel/lib/active_model/secure_password.rb

@@ -68,6 +68,7 @@ module ActiveModel
           validates_confirmation_of :password, if: ->{ password.present? }
         end
 
+        # This code is necessary as long as the protected_attributes gem is supported.
         if respond_to?(:attributes_protected_by_default)
           def self.attributes_protected_by_default #:nodoc:
             super + ['password_digest']