Add simple CONTRIBUTING.md (#1524)

Author: CvBlixen

CONTRIBUTING.md

@@ -0,0 +1,8 @@
+# Contributing to graphql-shield
+
+## Development setup
+
+1. [Fork](https://docs.github.com/en/get-started/quickstart/contributing-to-projects#forking-a-repository) and [clone](https://docs.github.com/en/get-started/quickstart/contributing-to-projects#cloning-a-fork) this repository.
+1. [Install pnpm](https://pnpm.io/installation).
+1. Run `pnpm install`.
+1. Run `pnpm test`. All tests should pass.

README.md

@@ -52,7 +52,7 @@ Support this project by becoming a sponsor. Your logo will show up here with a l
 
 ## Contributing
 
-We are always looking for people to help us grow `graphql-shield`! If you have an issue, feature request, or pull request, let us know!
+We are always looking for people to help us grow `graphql-shield`! If you have an issue, feature request, or pull request, let us know! For information about development setup and more, see [CONTRIBUTING.md](CONTRIBUTING.md).
 
 ## License