improve contributing docs [skip ci]

Author: SpaceK33z

CONTRIBUTING.md

@@ -14,3 +14,7 @@ If you want to use a GraphQL Playground to test something by hand, you can go to
 # Adding a feature or changing behavior
 
 For features or changes, please create a new issue first. Since this is a very opinionated package, it is possible I don’t like the change. By discussing it first you can prevent wasted time. But please do! I am very open to improvements.
+
+# Publishing packages
+
+In the root repository, run `yarn run publish` (note: the `run` part is very important). This will make Lerna publish all the packages. After that, be sure to write a changelog on GitHubs Releases page.