add doc

Author: SiyaoIsHiding

query-builder/src/main/java/com/datastax/oss/driver/api/querybuilder/select/Select.java

@@ -166,7 +166,7 @@ default Select orderBy(@NonNull String columnName, @NonNull ClusteringOrder orde
   @NonNull
   Select orderByAnnOf(@NonNull String columnName, @NonNull CqlVector<?> ann);
 
-  /** Adds the ORDER BY ... ANN OF ... clause */
+  /** Adds the ORDER BY ... ANN OF ... clause, usually used for vector search */
   @NonNull
   Select orderByAnnOf(@NonNull CqlIdentifier columnId, @NonNull CqlVector<?> ann);
   /**