Correct Readme instructions how to customize the UI

As at the moment the Readme does not explain the structure of the code any more, the Readme has to be actualized.

(This is just a draft, to keep track of this Issue)

README.md

@@ -25,9 +25,14 @@ You can use matrix-react-sdk directly, but to do this you would have to provide
 How to customise the SDK
 ========================
 
-The SDK uses the 'atomic' design pattern as seen at http://patternlab.io to
+The SDK formerly used the 'atomic' design pattern as seen at http://patternlab.io to
 encourage a very modular and reusable architecture, making it easy to
 customise and use UI widgets independently of the rest of the SDK and your app.
+
+So unfortunately at the moment this document does not describe how to customize your UI!
+
+###This is the old description for the atomic design pattern:
+
 In practice this means:
 
  * The UI of the app is strictly split up into a hierarchy of components.