Document that a private constructor opts-out of constructor binding

Closes gh-34820

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/external-config.adoc

@@ -725,7 +725,7 @@ include::code:MyProperties[]
 In this setup, the presence of a single parameterized constructor implies that constructor binding should be used.
 This means that the binder will find a constructor with the parameters that you wish to have bound.
 If your class has multiple constructors, the `@ConstructorBinding` annotation can be used to specify which constructor to use for constructor binding.
-To opt out of constructor binding for a class with a single parameterized constructor, the constructor must be annotated with `@Autowired`.
+To opt out of constructor binding for a class with a single parameterized constructor, the constructor must be annotated with `@Autowired` or made `private`.
 Constructor binding can be used with records.
 Unless your record has multiple constructors, there is no need to use `@ConstructorBinding`.