Polishing: Clarified documentation about Endpoint Extensions

Signed-off-by: mipo256 <mikhailpolivakha@email.com>

Author: Mikhail Polivakha

documentation/spring-boot-docs/src/docs/antora/modules/reference/pages/actuator/endpoints.adoc

@@ -401,6 +401,8 @@ For example, javadoc:org.springframework.boot.actuate.endpoint.web.annotation.We
 You can write technology-specific extensions by using javadoc:org.springframework.boot.actuate.endpoint.web.annotation.EndpointWebExtension[format=annotation] and javadoc:org.springframework.boot.actuate.endpoint.jmx.annotation.EndpointJmxExtension[format=annotation].
 These annotations let you provide technology-specific operations to augment an existing endpoint.
 
+NOTE: As of now, it is possible to have only a single extension per an individual javadoc:org.springframework.boot.actuate.endpoint.annotation.Endpoint[format=annotation].
+
 Finally, if you need access to web-framework-specific functionality, you can implement servlet or Spring javadoc:org.springframework.stereotype.Controller[format=annotation] and javadoc:org.springframework.web.bind.annotation.RestController[format=annotation] endpoints at the cost of them not being available over JMX or when using a different web framework.