Add CONTRIBUTING.md

[kfcampbell]

This is the Go side of octokit/dotnet-sdk#37, and adds an appropriate CONTRIBUTING.md as well as a code of conduct.

👀 Rendered version 👀

[github-actions]

👋 Hi! Thank you for this contribution! Just to let you know, our GitHub SDK team does a round of issue and PR reviews twice a week, every Monday and Friday! We have a process in place for prioritizing and responding to your input. Because you are a part of this community please feel free to comment, add to, or pick up any issues/PRs that are labled with Status: Up for grabs. You & others like you are the reason all of this works! So thank you & happy coding! 🚀

[what-the-diff]

PR Summary

• Introduction of a Contribution Guide
  A new file, CONTRIBUTING.md, has been added to the project. This file serves as a comprehensive guide for anyone who is interested in contributing to this project. It helps streamline the collaboration process and ensures contributors understand the project rules.

• Creating Issues and Pull Requests Section
  This section in the guideline document instructs contributors on the successful creation of issues and pull requests. It ensures every contributor knows how to raise matters regarding the project effectively and contribute solutions.

• Detailed Guidance on Repository Forking and Local Changes
  Contributors can also get instructions on how to create a fork of the project (i.e., make their own version of the project) and make changes to the project on their local machines. This facilitates easier and more organized contribution to the project.

• Inclusion of Helpful Documentation Links
  For better understanding and to provide a comprehensive learning experience, the file includes links to other documentation. This enables contributors to have easy access to further information to guide their contributions.