Added reference to previous name (home-assistant#3637)

source/_components/input_number.markdown

@@ -13,6 +13,10 @@ ha_release: 0.16
 redirect_from: /components/input_slider/
 ---
 
+<p class='note'>
+Before version 0.55 this component was known as `input_slider` and did not have the `mode` configuration option.
+</p>
+
 The `input_number` component allows the user to define values that can be controlled via the frontend and can be used within conditions of automation. The frontend can display a slider, or a numeric input box. Changes to the slider or numeric input box generate state events. These state events can be utilized as `automation` triggers as well.
 
 To enable this input number in your installation, add the following lines to your `configuration.yaml`: