fix description for Sensor.Value interface

Since [1] was merged, the 'Value' property may be written to in some
situations. Update the documentation for this interface.

References:
[1] https://gerrit.openbmc.org/c/openbmc/phosphor-dbus-interfaces/+/36333

Change-Id: I534267bb3068c658929b48ca25ff0bb2e646e4f7
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>
diff --git a/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml b/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml
index 4196600..17d4621 100644
--- a/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml
+++ b/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml
@@ -18,7 +18,9 @@
     Any service implementing Sensor.Value on one or more objects must implement
     org.freedesktop.DBus.ObjectManager on /xyz/openbmc_project/sensors.
 
-    All Sensor.Value properties are read-only.
+    All Sensor.Value properties are read-only, unless the
+    xyz.openbmc_project.Sensor.ValueMutability interface is present on the same
+    object path. In that case, refer to the docs for ValueMutability interface.
 
 properties:
     - name: Value