Add documentation to Producer class
Add documentation to Producer class

geffzhang/kafka-net,EranOfer/KafkaNetClient,gigya/KafkaNetClient,PKRoma/kafka-net,martijnhoekstra/kafka-net,nightkid1027/kafka-net,aNutForAJarOfTuna/kafka-net,Jroland/kafka-net,CenturyLinkCloud/kafka-net,BDeus/KafkaNetClient,bridgewell/kafka-net