docs: Remove outdated links from README Getting Started section. (#1694)

Author: sgpinkus

Readme.md

@@ -40,9 +40,7 @@ app.listen(3000);
 ## Getting started
 
  - [Kick-Off-Koa](https://github.com/koajs/kick-off-koa) - An intro to Koa via a set of self-guided workshops.
- - [Workshop](https://github.com/koajs/workshop) - A workshop to learn the basics of Koa, Express' spiritual successor.
- - [Introduction Screencast](https://knowthen.com/episode-3-koajs-quickstart-guide/) - An introduction to installing and getting started with Koa
-
+ - [Guide](docs/guide.md) - Go straight to the docs.
 
 ## Middleware