Update vss.md. add INSTALL and LOAD to example.

docs/extensions/vss.md

@@ -13,6 +13,9 @@ See the [announcement blog post]({% post_url 2024-05-03-vector-similarity-search
 To create a new HNSW (Hierarchical Navigable Small Worlds) index on a table with an `ARRAY` column, use the `CREATE INDEX` statement with the `USING HNSW` clause. For example:
 
 ```sql
+INSTALL vss;
+LOAD vss;
+
 CREATE TABLE my_vector_table (vec FLOAT[3]);
 INSERT INTO my_vector_table SELECT array_value(a, b, c) FROM range(1, 10) ra(a), range(1, 10) rb(b), range(1, 10) rc(c);
 CREATE INDEX my_hnsw_index ON my_vector_table USING HNSW (vec);