Update README.md

Author: valerybugakov

README.md

@@ -2,6 +2,10 @@
 
 A toolkit for writing codemods powered by [ts-morph](https://github.com/dsherret/ts-morph) and [PostCSS](https://github.com/postcss/postcss).
 
+## Docs
+
+Extended documentation is coming to the project. In the meantime, take a look at [the RFC](https://docs.google.com/document/d/1SMxtA4O9vDVqBlAUFwFdxG2wXnDOId2gjAOWtdp3Zas/edit?usp=sharing), which contains all the background information.
+
 ## Setup
 
 ```sh