update readme

README.md

@@ -1,7 +1,29 @@
 # Bootstrap v4 integration for Kendo widgets
 
-Extends Bootstrap theme for use with Kendo UI widgets.
+TLDR: Theme Kendo UI widgets based on Bootstrap.
+
+_Longer version_: The project aims to provide a Bootstrap theme for Kendo UI widgets, that uses the same variables as Bootstrap to achieve **mostly** the same appearance and size.
 
 ## Building
 
 Install build dependencies via `npm install`. Run `npm run build` to build the css.
+
+## Customizing
+
+All variable handling happens in [_bootstrap-map.scss](src/_bootstrap-map.scss) and it loads Bootstrap variables from the default location e.g. `node_modules/bootstrap/scss/_variables.scss`.
+
+If you have customized version of Bootstrap, you need to specify the location in _bootstrap-map.scss. Then build as usual.
+
+## Troubleshooting
+
+Since Bootstrap is loaded as npm module pointing directly to the [v4 branch](https://github.com/twbs/bootstrap/tree/v4-dev) it's not impossible for something to break after update.
+
+If it's a mapped variable, you can patch it directly in _bootstrap-map.scss. If it's explicit variable, you need to patch all files.
+
+In any case, you can open an issue.
+
+## Under the hood
+
+To ensure some sort of compatibility, Bootstrap variables are mapped locally. Further more, that enables us to use a ad-hoc micro framework based on primitive widgets e.g. [button](src/mixins/appearance/_button.scss), [input](src/mixins/appearance/_input.scss), [node](src/mixins/appearance/_node.scss) etc.
+
+Not all variables are mapped though. Some, like `$tooltip-arrow-width`, used in tooltip, are referenced explictly, because they don't fit within the aforementioned framework.