improve contributing guidelines

Author: SpaceK33z

CONTRIBUTING.md

@@ -6,9 +6,10 @@ Pull requests and issues are very welcome!
 
 # Getting started
 
-To get started, clone this repository and run `yarn` or `npm i`.
+To get started, clone this repository and run `yarn` in the repository root. Note you have to use Yarn, npm will not work correctly.
 
-After that you can run the tests with `yarn test`.
+In the `packages/` folder, pick one of the packages you want to work on. You can run the tests inside a package with `yarn test`.
+If you want to use a GraphQL Playground to test something by hand, you can go to `packages/graphql-authentication-prisma/example` and run `docker-compose up -d` in it (this requires you have Docker installed). Then, run `yarn start`.
 
 # Adding a feature or changing behavior