Add endpoint documentation for the storage-efficiency field

Signed-off-by: F.N. Claessen <felix@seita.nl>

flexmeasures/api/v3_0/sensors.py

@@ -271,6 +271,7 @@ def trigger_schedule(  # noqa: C901
         at which the state of charge (soc) is 12.1 kWh, with a target state of charge of 25 kWh at 4.00pm.
         The minimum and maximum soc are set to 10 and 25 kWh, respectively.
         Roundtrip efficiency for use in scheduling is set to 98%.
+        Storage efficiency is set to 99.99%, denoting the state of charge left after each time step equal to the sensor's resolution.
         Aggregate consumption (of all devices within this EMS) should be priced by sensor 9,
         and aggregate production should be priced by sensor 10,
         where the aggregate power flow in the EMS is described by the sum over sensors 13, 14 and 15
@@ -294,6 +295,7 @@ def trigger_schedule(  # noqa: C901
                     "soc-min": 10,
                     "soc-max": 25,
                     "roundtrip-efficiency": 0.98,
+                    "storage-efficiency": 0.9999,
                 },
                 "flex-context": {
                     "consumption-price-sensor": 9,