Update dispatch.proto to clarify payload usage

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

proto/frequenz/api/dispatch/v1/dispatch.proto

@@ -197,6 +197,23 @@ message DispatchData {
   //      - The data should not contain executable code or scripts.
   //      - Ensure all data is properly sanitized and encoded.
   //      - The total size of the payload should not exceed 50 KB.
+  //
+  // The payload is expected to follow a specific format that the downstream applications consuming the dispatch API
+  // are responsible for understanding and processing.
+  //
+  // Example JSON payload:
+  // {
+  //   "settings": {
+  //     "power_max": 10,   // Maximum power level for the dispatch (in kW)
+  //     "soc_min": 20,     // Minimum state of charge for battery storage (in %)
+  //     "soc_max": 80      // Maximum state of charge for battery storage (in %)
+  //   }
+  // }
+  //
+  // In this example, a microgrid could use this payload to set operational parameters such as the maximum power output
+  // of a solar PV array or the charge/discharge limits of a battery storage system. This flexibility allows the microgrid
+  // to dynamically adjust its behavior based on the current needs or conditions, such as optimizing battery usage or
+  // limiting PV output during low demand periods.
   google.protobuf.Struct payload = 7;
 
   // The recurrence rule