sensor: add relative humidity

Change-Id: I84f37194adbcaf99b4c426a8d51afc738bd6a799
diff --git a/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml b/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml
index c593653..2af3f67 100644
--- a/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml
+++ b/yaml/xyz/openbmc_project/Sensor/Value.interface.yaml
@@ -8,6 +8,7 @@
       current
       energy
       fan_tach
+      humidity
       power
       pressure
       temperature
@@ -43,6 +44,7 @@
           For objects in the current namespace, Unit must be "Amperes".
           For objects in the energy namespace, Unit must be "Joules".
           For objects in the fan_tach namespace, Unit must be "RPMS".
+          For objects in the humidity namespace, Unit must be "PercentRH"
           For objects in the power namespace, Unit must be "Watts".
           For objects in the pressure namespace, Unit must be "Pascals"
           For objects in the temperature namespace, Unit must be "DegreesC".
@@ -72,6 +74,9 @@
         - name: Percent
           description: >
             Resource utilization as a percentage.
+        - name: PercentRH
+          description: >
+            Relative humidity as a percentage.
         - name: Pascals
           description: >
             Pressure as pascals.