GH-1846 Update documentation on 'splittable' attribute of PollableBean
GH-1846 Update documentation on 'splittable' attribute of PollableBean

Resolves #1846

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