better mention message_hash

Author: Ivansete-status

standards/application/reliable-channel-api.md

@@ -111,7 +111,7 @@ See [SEGMENTATION](./segmentation.md).
 - Each new segment to be sent, requires the following data:
   - `MessageId`: a keccak-256([message](https://lip.logos.co/ift-ts/raw/sds.html#message)'s content) hex string (e.g. `4e03657aea45a94fc7d47ba826c8d667c0d1e6e33a64a036ec44f58fa12d6c45`), generated by the Reliable Channel API.
   - `ChannelId`: the `channelId` passed to `createReliableChannel`.
-  - `Retrieval hint`: the transport `MessageHash` of previous segments, exposed by the underlying [MESSAGING-API](/standards/application/messaging-api.md) upon ``MessageSendPropagatedEvent` reception.
+  - `Retrieval hint`: the transport `MessageHash` of previous segments, mentioned as `message_hash` in [MESSAGING-API](/standards/application/messaging-api.md), upon ``MessageSendPropagatedEvent` reception.
   The hint provider registered during [Node initialization](#node-initialization) performs this `MessageId → MessageHash` lookup. In turn, that mapping MUST be persisted by SDS using the `persistence` backend configured in `SdsConfig`.
 
 - Each sent segment is added to an outgoing buffer.