Add saveWidget to highcharter demo in Readme.md

Change-Id: I6abe913a7c9237bad75dbca3e16a4235e1ea82bf
diff --git a/Readme.md b/Readme.md
index 4dabed6..74f65af 100644
--- a/Readme.md
+++ b/Readme.md
@@ -22,8 +22,11 @@
 library(tidyverse)
 library(highcharter)
 library(idsThemeR)
-highcharts_demo() %>%
+library(htmlwidgets)
+hc <- highcharts_demo() %>%
    hc_add_theme(hc_theme_ids_light(palette = "ids"))
+print(hc)
+saveWidget(hc, file="highchart.html")
 ```
 ![](./man/figures/Readme-Example-1.png)<!-- -->