Fix incorrect constructor docstring for IndexScalarQuantizer

Author: hckex

faiss/IndexScalarQuantizer.h

@@ -29,8 +29,8 @@ struct IndexScalarQuantizer : IndexFlatCodes {
     /** Constructor.
      *
      * @param d      dimensionality of the input vectors
-     * @param M      number of subquantizers
-     * @param nbits  number of bit per subvector index
+     * @param qtype  type of scalar quantizer (e.g., QT_4bit)
+     * @param metric distance metric used for search (default: METRIC_L2)
      */
     IndexScalarQuantizer(
             int d,