Fix readme example

readme.md

@@ -79,7 +79,7 @@ Use factories (sync and async) if service requires special initialization or cle
 ```python
 @service
 async def make_db(dsn: Annotated[str, Inject(param="db_dsn")]) -> AsyncIterator[Connection]:
-    async with DB(dsn) as conn:
+    async with Connection(dsn) as conn:
         yield conn
 ```