Create CONTRIBUTING.md (#8)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

.github/CONTRIBUTING.md

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+# Contributing
+
+Thank you for contributing! It's very appreciated. ♥️
+Please verify that you can check the following boxes.
+
+## Before opening a PR
+
+- [ ] The PR has a defined scope, it changes one thing (and not any unrelated other)
+- [ ] If it is a bug fix, there is an opened issue<sup>1</sup>
+
+<sup>1</sup> If no issue exists about the bug, don't hesitate to open one~
+
+## Once the PR is opened
+
+- [ ] If it is a bug fix, you tagged the related issue in the PR title<sup>2</sup>
+- [ ] If needed, you wrote the reasons of your change(s) in the PR description
+- [ ] The Rust GHA workflow status passes<sup>3</sup>
+
+<sup>2</sup> The recommended formatting is: `GH-XXX: <title>` with `XXX` being the issue number.
+<sup>3</sup> The pre-commit CI status does not have to pass, but it's better if it does 💕
+
+### Suggested, but not enforced:
+
+- [ ] The changes you made are in a separate branch (i.e. not your fork's `main`)
+
+## Once the PR is merged
+
+Thank you again~ Your contribution is very valuable.
+You can now delete your branch safely. 😄
+
+## My PR got closed...
+
+We cherish your willingness to participate to the project!
+Perhaps your PR did not meet the requirements or another path was chosen.
+
+Don't get discouraged! Your future PRs will be looked at in detail and one of them might get merged~
+
+**Happy coding~**