[features] add messages reading guide

Author: capcom6

docs/features/reading-messages.md

@@ -0,0 +1,28 @@
+# Reading Messages
+
+The app not only allows receiving incoming messages in real-time via webhooks but also enables reading previously received messages using the same webhook.
+
+## How it works
+
+To read messages, please follow these steps:
+
+1. Register the `sms:received` webhook as described in the [Webhooks](../features/webhooks.md) guide if you haven't done so already.
+2. Determine the Device ID of the device you want to read messages from by calling the `GET /devices` endpoint:
+    ```
+    curl -u <username>:<password> https://api.sms-gate.app/3rdparty/v1/devices
+    ```
+3. Send a request with `deviceId` and period to the `POST /messages/inbox/export` endpoint:
+    ```
+    curl -u <username>:<password> \
+      -H "Content-Type: application/json" \
+      -d '{ "deviceId": "<device-id>", "since": "2024-01-01T00:00:00Z", "until": "2024-12-31T23:59:59Z" }' \
+      https://api.sms-gate.app/3rdparty/v1/messages/inbox/export
+    ```
+4. After receiving the request, the device will send `sms:received` webhooks for each message in the inbox for the specified period.
+
+## Notes
+
+* The webhook will be sent for each message independently, so the order of messages is not guaranteed.
+* It is recommended to split long periods into shorter ones to avoid excessive load on your webhook receiver.
+* The export webhooks retry policy is the same as described in the [Webhooks](../features/webhooks.md) guide.
+* The ID for incoming messages is generated based on the content of the message and is not guaranteed to be unique.

docs/features/webhooks.md

@@ -7,6 +7,7 @@ Webhooks offer a powerful mechanism to receive real-time notifications of events
 Currently, the following event is supported:
 
 - `sms:received` - Triggered when an SMS is received by the device. The payload for this event includes:
+    * `messageId`: The ID of the SMS message. The ID is generated based on the content of the message and is not guaranteed to be unique.
     * `message`: The content of the SMS message.
     * `phoneNumber`: The phone number that sent the SMS.
     * `simNumber`: The SIM card number that received the SMS. May be `null` on some Android devices.

mkdocs.yml

@@ -45,6 +45,7 @@ nav:
   - Features:
       - Multi-SIM Support: features/multi-sim.md
       - Webhooks: features/webhooks.md
+      - Reading Messages: features/reading-messages.md
       - Logging: features/logging.md
   - Pricing: pricing.md
   - Privacy: