docs: add link

Author: PanJiaChen

src/styles/variables.scss

@@ -22,6 +22,7 @@ $subMenuHover:#001528;
 $sideBarWidth: 180px;
 
 // the :export directive is the magic sauce for webpack
+// https://www.bluematador.com/blog/how-to-share-variables-between-js-and-sass
 :export {
   menuText: $menuText;
   menuActiveText: $menuActiveText;