readme: link the tutorial doc in README (#10)

Summary:
The tutorial is pretty good but not linked in the README. Adding it to README will enhance discoverability.

Pull Request resolved: #10

Reviewed By: abesto

Differential Revision: D59059268

Pulled By: ukautz

fbshipit-source-id: c6809ab4c638b038e60bb2623e8aeedb9dd14704

README.md

@@ -38,6 +38,8 @@ $ acme --version > /dev/null
 ```
 ````
 
+To start using Scrut, see the [Tutorial](https://facebookincubator.github.io/scrut/docs/tutorial/) page for a walkthrough of Scrut use from start to end.
+
 ## Contribute
 
 - [Contributing](CONTRIBUTING.md)