chore: add contributing.md

CONTRIBUTING.md

@@ -0,0 +1,47 @@
+# Contributing
+
+Thanks for taking the time to contribute to this project! If you'd like to learn
+how the API works, check out the (unofficial)
+[documentation](https://classchartsapi.github.io/api-docs/).
+
+## Dev Setup
+
+### Requirements
+
+- [Deno](https://deno.land/) (for the main development)
+- [Node.js](https://nodejs.org/en/) (for testing the NPM package)
+- [pnpm](https://pnpm.io/) (for installing dependencies for the NPM package)
+
+### Instructions
+
+To contribute to this repo, you will need to fork the repo first. Click the fork
+button in the top right corner of the repo page.
+
+1. Clone your forked repo to your local machine
+
+```bash
+git clone https://github.com/<your_github_username>/classcharts-api-js.git
+cd classcharts-api-js
+```
+
+### Testing
+
+When adding a new function, if you can, add a test for it. Tests are located in
+`[FILENAME]_test.ts`.\
+To run the tests, run:
+
+```bash
+deno test -A
+```
+
+The NPM package will automatically be tested when you build it.
+
+### Building
+
+The Deno module is already built but to compile and test the NPM package, run:
+
+```bash
+deno task npm 1.0.0
+```
+
+Make sure to replace `1.0.0` with the version number.