Added EXPLAIN ANALYZE to readme [skip ci]

README.md

@@ -175,6 +175,12 @@ To speed up queries with an index, increase the number of inverted lists (at the
 CREATE INDEX ON items USING ivfflat (embedding vector_l2_ops) WITH (lists = 1000);
 ```
 
+Use `EXPLAIN ANALYZE` to debug performance
+
+```sql
+EXPLAIN ANALYZE SELECT * FROM items ORDER BY embedding <-> '[3,1,2]' LIMIT 1;
+```
+
 ## Reference
 
 ### Vector Type