Update API.md

Author: marcobambini

API.md

@@ -92,9 +92,11 @@ SELECT vector_init('documents', 'embedding', 'dimension=384,type=FLOAT32,distanc
 
 ## `vector_quantize(table, column, options)`
 
-**Returns:** `NULL`
+**Returns:** `INTEGER`
 
 **Description:**
+Returns the total number of succesfully quantized rows.
+
 Performs quantization on the specified table and column. This precomputes internal data structures to support fast approximate nearest neighbor (ANN) search.
 Read more about quantization [here](https://github.com/sqliteai/sqlite-vector/blob/main/QUANTIZATION.md).