Update 0.8-upgrade.md

docs/0.8-upgrade.md

@@ -26,7 +26,32 @@ builds. ClojureScript compiler will automatically set this constant to
 `production` value when using `:advanced` optimizations. This enables
 the React production build.
 
-## NodeJS
+## Browser - loading React from CDNJS or custom Webpack bundle
+
+**TODO: Not tested properly**
+
+If you want to load React.js yourself from external JS file (CDN) or from custom bundle,
+it should be possible to override the Cljsjs foreign-libs, while still using externs from Cljsjs packages. To override the foreign-libs, you can provide following compiler option:
+
+```clj
+:foreign-libs
+ [{:file "empty.js",
+   :provides ["react" "react-dom" "create-react-class" "react-dom/server"],
+   :requires [],
+   :global-exports '{react React, react-dom ReactDOM, create-react-class createReactClass, react-dom/server ReactDOMServer}}]
+```
+
+You'll also need to create the mentioned `empty.js` file (FIXME: relative to `project.clj`?).
+
+If your bundle provides other libraries, you could extern `:provides` and `:global-exports` (e.g. `prop-types`).
+
+## NodeJS - Cljsjs
+
+Requires https://github.com/clojure/clojurescript/commit/f7d611d87f6ea8a605eae7c0339f30b79a840b49
+
+Reagent should use Cljsjs libraries by default even when running on Node.
+
+## NodeJS - node modules
 
 Install `react`, `react-dom` and `create-react-class` npm packages,
 and ClojureScript should automatically use `require` to