Chore(contributing): introduce contribution guideline

CONTRIBUTING.MD

@@ -0,0 +1,56 @@
+# Contributing guide
+
+Thanks for your contribution 🥳 to the Fastily website redesign project!
+
+[Code of Conduct](https://github.com/fastify/.github/blob/main/CODE_OF_CONDUCT.md)
+
+* [Vocabulary](#vocabulary)
+* [Commit message guidelines](#commit-message-guidelines)
+* [Pull Request Policy](#pull-request-policy)
+* [Before merging](#before-merging)
+* [Becoming a collaborator](#becoming-a-collaborator)
+* [Debugging failing checks](#debugging-failing-checks)
+* [Developer's Certificate of Origin 1.1](#developers-certificate-of-origin-11)
+
+
+## Pull Request Policy
+
+### Before merging
+
+This repository follows the same rules as a fastify plugin repository. A detailed process is explained at [fastify/CONTRIBUTING.md#rules](https://github.com/fastify/fastify/blob/main/CONTRIBUTING.md#rules)
+
+## Vocabulary
+
+* A **Contributor** is any individual who creates an issue/PR, comments on an issue/PR
+  or contributes in some other way.
+* A **Collaborator** is a contributor with write access to the repository. See [here](#becoming-a-collaborator) on how to become a collaborator.
+
+## Becoming a collaborator
+
+We follow the [Fastify organization Governance model](https://github.com/fastify/fastify/blob/main/GOVERNANCE.md#collaborator-nominations) so it is necessary to contribute to this repository in order to become a member.
+
+## Debugging failing checks
+
+* For failing formatting or linting, try running:
+
+```bash
+npm run format
+```
+
+## Developer's Certificate of Origin 1.1
+
+By contributing to this project, I certify that:
+
+* (a) The contribution was created in whole or in part by me and I have the right to
+  submit it under the open source license indicated in the file; or
+* (b) The contribution is based upon previous work that, to the best of my knowledge,
+  is covered under an appropriate open source license and I have the right under that
+  license to submit that work with modifications, whether created in whole or in part
+  by me, under the same open source license (unless I am permitted to submit under a
+  different license), as indicated in the file; or
+* (c) The contribution was provided directly to me by some other person who certified
+  (a), (b) or (c) and I have not modified it.
+* (d) I understand and agree that this project and the contribution are public and that
+  a record of the contribution (including all personal information I submit with it,
+  including my sign-off) is maintained indefinitely and may be redistributed consistent
+  with this project or the open source license(s) involved.