Make changes according to comments.

Author: Bingqin Zhou

kcbq-api/src/main/java/com/wepay/kafka/connect/bigquery/api/KafkaSchemaRecordType.java

@@ -1,6 +1,9 @@
 package com.wepay.kafka.connect.bigquery.api;
 
 
+/**
+ *  Enum class for Kafka schema or record type, either value or key.
+ */
 public enum KafkaSchemaRecordType {
 
     VALUE("value"),

kcbq-connector/src/main/java/com/wepay/kafka/connect/bigquery/SchemaManager.java

@@ -1,7 +1,13 @@
 package com.wepay.kafka.connect.bigquery;
 
 
-import com.google.cloud.bigquery.*;
+import com.google.cloud.bigquery.BigQuery;
+import com.google.cloud.bigquery.Field;
+import com.google.cloud.bigquery.LegacySQLTypeName;
+import com.google.cloud.bigquery.StandardTableDefinition;
+import com.google.cloud.bigquery.TableId;
+import com.google.cloud.bigquery.TableInfo;
+import com.google.cloud.bigquery.TimePartitioning;
 import com.wepay.kafka.connect.bigquery.api.KafkaSchemaRecordType;
 import com.wepay.kafka.connect.bigquery.api.SchemaRetriever;
 import com.wepay.kafka.connect.bigquery.convert.KafkaDataBuilder;

kcbq-connector/src/main/java/com/wepay/kafka/connect/bigquery/config/BigQuerySinkConfig.java

@@ -574,15 +574,23 @@ public SchemaRetriever getSchemaRetriever() {
 
   /**
    *
-   * @return An optional class of KafkaKeyFieldName.
+   * If the connector is configured to load Kafka data into BigQuery, this config defines
+   * the name of the kafka data field. A structure is created under the field name to contain
+   * kafka data schema including topic, offset, partition and insertTime.
+   *
+   * @return Field name of Kafka Data to be used in BigQuery
    */
   public Optional<String> getKafkaKeyFieldName() {
     return Optional.ofNullable(getString(KAFKA_KEY_FIELD_NAME_CONFIG));
   }
 
   /**
    *
-   * @return An optional class of KafkaDataFieldName.
+   * If the connector is configured to load Kafka keys into BigQuery, this config defines
+   * the name of the kafka key field. A structure is created under the field name to contain
+   * a topic's Kafka key schema.
+   *
+   * @return Field name of Kafka Key to be used in BigQuery
    */
   public Optional<String> getKafkaDataFieldName() {
     return Optional.ofNullable(getString(KAFKA_DATA_FIELD_NAME_CONFIG));