Link css-spatial from index

Author: fantasai

README.md

@@ -13,6 +13,7 @@ This repo is a place where WebKit contributors may post [explainers](https://www
 * [TrackConfiguration API](TrackConfiguration/)
 * [UndoManager API](UndoManager/)
 * [Spatial Backdrop](spatial-backdrop/)
+* [CSS Spatial Layout](css-spatial/explainer.md)
 
 ## Graduates
 

css-spatial/explainer.md

@@ -7,7 +7,7 @@
 ## Participate
 - https://github.com/WebKit/explainers
 
-## Specification
+## Specification Draft
 - https://webkit.github.io/explainers/css-spatial/Overview.html
 
 ## Table of Contents