Create CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1,13 @@
+# Contributing
+
+[issue-url]: https://github.com/control-toolbox/OptimalControl.jl/issues
+[first-good-issue-url]: https://github.com/control-toolbox/OptimalControl.jl/contribute
+
+If you think you found a bug or if you have a feature request or suggestion, feel free to open an [issue][issue-url].
+Before opening a pull request, start an issue or a discussion on the topic, please. 
+
+Any contributions are welcomed, check out [how to contribute to a Github project](https://docs.github.com/en/get-started/exploring-projects-on-github/contributing-to-a-project). 
+If it is your first contribution, you can also check [this first contribution tutorial](https://github.com/firstcontributions/first-contributions).
+You can find first good issues, if any, at the [first good issues page][first-good-issue-url]. You may find other packages to contribute to at the [control-toolbox organization](https://github.com/control-toolbox).
+
+If you want to ask a question, feel free to start a discussion [here](https://github.com/orgs/control-toolbox/discussions). This forum is for general discussion about this repository and the [control-toolbox organization](https://github.com/control-toolbox), so questions about any of our packages are welcome.