Update readme

readme.md

@@ -3,10 +3,28 @@
 A simple proof-of-concept implementation of a mechanism to pull outside styles
 into a Shadow-DOM.
 
-## Features:
+## Rationale
+
+This is primarily meant as a simple proof-of-concept to show how this mechanism
+could work as a solution to the [use-case](https://github.com/WICG/webcomponents/issues/909)
+of authors wanting to let outside styling rules affect content inside a shadow
+DOM.
+
+The aim of this project is not to provide a full solution to the problem, but to
+showcase how one possible solution could work and to allow playing around with
+the concept in real-world projects.
+
+## Notes
+
+Due to this being a relatively "simple" javascript implementation, outside
+selectors will simply be mirrored into the shadow DOM, but more complex
+selectors like child selectors won't match elements across shadow DOM
+boundaries.
+
+## Planned Features:
 
 - [x] Import `<link>` tags
 - [x] Import `<style>` tags
 - [x] Import into layer
-- [ ] Import from layer
 - [x] Automatic updating
+- [ ] Import from layer