[EventHubs] Add note to migration guide to clarify incompatibility of V1 and V5 checkpoints
Ideally (for future work) we could give a small snippet of code to demonstrate the transformation needed to accompany this warning.
@@ -132,6 +132,13 @@ your program when receiving events.
In V5, `EventHubConsumerClient` allows you to do the same with the `receive()` method if you
pass a `CheckpointStore` to the constructor.
+> **Note:** V1 checkpoints are not compatible with V5 checkpoints.
+If pointed at the same blob, consumption will begin at the first message.
+V1 checkpoint json in the respective blobs can be manually converted (per-partition) if needed.
+In V1 checkpoints (sequence_number and offset) are stored in the format of json along with ownership information
+as the content of the blob, while in V5, checkpoints are kept in the metadata of a blob and the metadata is composed of name-value pairs.
+Please check [update_checkpoint](https://github.com/Azure/azure-sdk-for-python/blob/master/sdk/eventhub/azure-eventhub-checkpointstoreblob/azure/eventhub/extensions/checkpointstoreblob/_blobstoragecs.py#L231-L250) in V5 for implementation detail.
+
So in V1:
```python
import logging
