add missing snippet for disabled slider

snippets/disabled_slider.html

 <label>Disabled <input type="checkbox" ng-model="slider.options.disabled"></label>
-<rzslider rz-slider-model="slider.value"
+<rzslider rz-slider-model="slider.minValue"
+          rz-slider-high="slider.maxValue"
           rz-slider-options="slider.options"></rzslider>

snippets/disabled_slider.js

 $scope.slider = {
-  value: 50,
+  minValue: 20,
+  maxValue: 80,
   options: {
     floor: 0,
     ceil: 100,
-    disabled: true
+    step: 10,
+    disabled: true,
+    showTicks: true, // just to show the disabled style
+    draggableRange: true // just to show the disabled style
   }
 };