Core refdoc proof read and update (#1344)
Core refdoc proof read and update (#1344)

related #1318
core refdoc update and proof read
GoogleCloudPlatform/spring-cloud-gcp,spring-cloud/spring-cloud-gcp,GoogleCloudPlatform/spring-cloud-gcp,GoogleCloudPlatform/spring-cloud-gcp,spring-cloud/spring-cloud-gcp,GoogleCloudPlatform/spring-cloud-gcp,GoogleCloudPlatform/spring-cloud-gcp,spring-cloud/spring-cloud-gcp,spring-cloud/spring-cloud-gcp