Fix the SQLAlchemy Item class

Author: pamelafox

README.md

@@ -138,6 +138,8 @@ Add a vector column
 from pgvector.sqlalchemy import Vector
 
 class Item(Base):
+ __tablename__ = "items"
+ id: Mapped[int] = mapped_column(primary_key=True)
  embedding = mapped_column(Vector(3))
 ```