more upgrade notes

Author: ryanflorence

upgrade-guides/v2.0.0.md

@@ -4,12 +4,16 @@
 
 ### Goals
 
+You might enjoy reading this issue: https://github.com/rackt/react-router/issues/2646
+
 1. Clear up the coupling between History and Router with simpler APIs.
 
 2. Provide cleaner integrations with other libraries like Redux, Relay, Async Props etc.
 
 3. Stop providing API that conceals usage of `context`. It is now a documented feature of React so developers using Router can implement their own opinions on how best to use context: Mixins, higher-order components, decorators, etc. React Router no longer has an opinion, but instead uses the lowest level feature of React.  This project wants to be an incredibly useful routing library and doesn't want to get hung up on best-practice patterns for getting stuff from up top to down low.
 
+4. Draw a clean line between what goes to Route Components as `props` and what goes on `context`.
+
 For more information see [https://github.com/rackt/react-router/issues/2646]
 
 For a lot of apps this upgrade might look like API churn. Underneath the hood there are significant differences that make integrating with the rest of the React ecosystem more straightforward. Thanks for your continued patience and support as we all build this tool together. It's hard to imagine the top-level API changing much after this. But if it does, rest assured we are committed to ...