chore(build): added example SASS file for variables

Author: mariuszm

src/sass/_includes.scss

@@ -2,5 +2,7 @@
 // @import '../../vendor/bootstrap-sass-official/vendor/assets/stylesheets/bootstrap/_normalize';
 // @import '../../vendor/bootstrap-sass-official/vendor/assets/stylesheets/bootstrap/_print';
 
+@import 'includes/variables';
+
 @import '../../vendor/bootstrap-sass-official/vendor/assets/stylesheets/bootstrap';
 @import '../../vendor/bootstrap-sass-official/vendor/assets/stylesheets/bootstrap/_theme';

src/sass/includes/_variables.scss

@@ -0,0 +1 @@
+$icon-font-path: 'vendor/bootstrap-sass-official/vendor/assets/fonts/bootstrap/' !default;