Better link to documentation and tutorials in README.md (#2032)

Summary:
Pull Request resolved: #2032

Better link to Recoil documentation and third-party tutorials in the NPM and GitHub `README.md`.

Reviewed By: wd-fb

Differential Revision: D39778651

fbshipit-source-id: e8bff0e1d7444ecc0a2ef1ec39ee129373e93b00

README.md

@@ -2,7 +2,17 @@
 
 Recoil is an experimental state management framework for React.
 
-Please see the website: https://recoiljs.org
+Website: https://recoiljs.org
+
+## Documentation
+
+Documentation: https://recoiljs.org/docs/introduction/core-concepts
+
+
+API Reference: https://recoiljs.org/docs/api-reference/core/RecoilRoot
+
+
+Tutorials: https://recoiljs.org/resources
 
 ## Installation