Fix async code examples

Author: febus982

docs/index.md

@@ -73,7 +73,7 @@ o = MyModel()
 o.name = "John"
 with sa_manager.get_session() as session:
     session.add(o)
-    session.commit()
+    await session.commit()
 ```
 
 /// details | Long lived sessions and multithreading

docs/manager/config.md

@@ -82,7 +82,7 @@ The interfaces are exactly the same, however you'll need to `await` the relevant
 ```python
 async with sa_manager.get_session() as session:
     session.add(o)
-    session.commit()
+    await session.commit()
 ```
 
 Note that async implementation has several differences from the sync one, make sure