feat: add CONTRIBUTING.md for newcomers

CONTRIBUTING.md

@@ -0,0 +1,13 @@
+# Contributing to create-t3-app
+
+## Contribution guidelines
+- Be respectful, civil, and open-minded.
+- Before opening a new pull request, try searching through the [issue tracker](https://github.com/nexxeln/create-t3-app/issues) for known issues or fixes.
+
+## How to contribute
+1. [Fork this repository](https://docs.github.com/en/get-started/quickstart/fork-a-repo) to your own GitHub account, then [clone the repository](https://docs.github.com/en/repositories/creating-and-managing-repositories/cloning-a-repository) to your machine.
+2. Follow the [README](https://github.com/nexxeln/create-t3-app#readme) to install the project.
+3. Create a new branch and implement your changes.
+4. Open a pull request!
+
+Thanks to Next.js. This contribution guide is inspired by the [Next.js contribution guide.](https://github.com/vercel/next.js/blob/canary/contributing.md)