Update readme

Author: nomcopter

README.md

@@ -8,6 +8,8 @@ react-mosaic is written in TypeScript and provides typings but can be used in Ja
 
 The best way to see it is a simple [**Demo**](https://palantir.github.io/react-mosaic/).
 
+v1.0 just released! Upgrade guide [here](./releases/tag/v1.0.0).
+
 #### Screencast
 [![screencast demo](./screencast.gif)](./screencast.gif)