GH-1710 Added note on adding custom Validator
GH-1710 Added note on adding custom Validator

Resolves #1710

spring-cloud/spring-cloud-stream,garyrussell/spring-cloud-stream,spring-cloud/spring-cloud-stream,garyrussell/spring-cloud-stream,garyrussell/spring-cloud-stream,spring-cloud/spring-cloud-stream,ilayaperumalg/spring-cloud-stream,ilayaperumalg/spring-cloud-stream