add scala doc

Author: xusliebana

src/main/scala/com/johnsnowlabs/nlp/HasMultipleInputAnnotationCols.scala

@@ -16,16 +16,20 @@
 
 package com.johnsnowlabs.nlp
 
-import com.johnsnowlabs.nlp.AnnotatorType.CHUNK
-import org.apache.spark.ml.param.{Params, StringArrayParam}
-import org.apache.spark.sql.types.StructType
-
+/**
+ * Trait  used to create annotators with input columns of variable length.
+ * */
 trait HasMultipleInputAnnotationCols extends HasInputAnnotationCols {
 
+  /** Annotator reference id. The Annotator type is the same for any of the input columns*/
   val inputAnnotatorType: String
 
   lazy override val inputAnnotatorTypes: Array[String] = getInputCols.map(_ =>inputAnnotatorType)
 
+  /**
+    * Columns that contain annotations necessary to run this annotator
+    * AnnotatorType is the same for all input columns in that annotator.
+    */
   override def  setInputCols(value: Array[String]): this.type = {
     set(inputCols, value)
   }