Add slides to root README

Author: s0

README.md

@@ -7,6 +7,8 @@ at OSCON 2019.
 
 Contents in [typescript-js-ecosystem](typescript-js-ecosystem).
 
+Slides are both available [as a pdf](typescript-js-ecosystem/slides.pdf) and on [google slides](https://docs.google.com/presentation/d/1OoHS-kvFStrSEte8uKvIVFZMiGR9fm2FO_rMB1RC2hc/edit?usp=sharing).
+
 ## [Writing npm (JavaScript) libraries using TypeScript](https://conferences.oreilly.com/oscon/oscon-or/public/schedule/detail/75953)
 
 Contents in [writing-npm-libraries-using-typescript](writing-npm-libraries-using-typescript).