Add temporary warning to readme.md

Author: wooorm

readme.md

@@ -1,5 +1,13 @@
 # remark-github [![Build Status](https://img.shields.io/travis/wooorm/remark-github.svg)](https://travis-ci.org/wooorm/remark-github) [![Coverage Status](https://img.shields.io/codecov/c/github/wooorm/remark-github.svg)](https://codecov.io/github/wooorm/remark-github)
 
+> :warning: **mdast is currently being renamed to remark** :warning:
+>
+> This means all plug-ins and relating projects change too, causing many
+> changes across the ecosystem. Expect the dust to settle in roughly a day.
+>
+> See this project at the previous stable commit
+> [c4a51d1](https://github.com/wooorm/remark-github/commit/c4a51d1).
+
 Auto-link references to commits, issues, pull-requests, and users like GitHub: [Writing on GitHub](https://help.github.com/articles/writing-on-github/#references).
 
 ## Installation