dts: binding: sensor: bq274xx: improve desc.

Improve descriptions of taper-current and terminate-voltage.
Also fixes units of taper-current.

Signed-off-by: Nick Ward <nix.ward@gmail.com>

dts/bindings/sensor/ti,bq274xx.yaml

@@ -24,12 +24,16 @@ properties:
   taper-current:
     type: int
     required: true
-    description: Battery Taper current in mAh
+    description: |
+      Current in mA slightly higher than the taper current threshold at which
+      point the charger cuts off charging.
 
   terminate-voltage:
     type: int
     required: true
-    description: Battery Terminate Voltage in mV
+    description: |
+      Minimum operating voltage of your system. This is the target where the
+      gauge typically reports 0% capacity. In mV.
 
   chemistry-id:
     type: int