[WIP] Add CONTRIBUTING and Code of conduct

.github/CODE_OF_CONDUCT.md

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+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnicity, sex characteristics, gender identity and expression,
+level of experience, education, socio-economic status, nationality, personal
+appearance, race, religion, or sexual identity and orientation.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+- Using welcoming and inclusive language
+- Being respectful of differing viewpoints and experiences
+- Gracefully accepting constructive criticism
+- Focusing on what is best for the community
+- Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+- The use of sexualized language or imagery and unwelcome sexual attention or
+  advances
+- Trolling, insulting/derogatory comments, and personal or political attacks
+- Public or private harassment
+- Publishing others' private information, such as a physical or electronic
+  address, without explicit permission
+- Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or
+reject comments, commits, code, wiki edits, issues, and other contributions
+that are not aligned to this Code of Conduct, or to ban temporarily or
+permanently any contributor for other behaviors that they deem inappropriate,
+threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by project maintainers.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported by contacting the project team. All complaints will be reviewed and
+investigated and will result in a response that is deemed necessary and
+appropriate to the circumstances. The project team is obligated to maintain
+confidentiality with regard to the reporter of an incident. Further details of
+specific enforcement policies may be posted separately.
+
+Project maintainers who do not follow or enforce the Code of Conduct in good
+faith may face temporary or permanent repercussions as determined by other
+members of the project's leadership.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4,
+available at https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
+
+[homepage]: https://www.contributor-covenant.org

.github/CONTRIBUTING.md

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+# CONTRIBUTING
+
+Thank you for taking the time to read how to contribute to our project! This is the basic guideline for contributing to [Marp team owned projects][marp-team].
+
+You can start contributing our project in several way like improve docs, report bug, request feature, writing code, and so on.
+
+Depending on the project you want to contribute, it might have additional guidelines you should follow at that repository. Please also check the guideline per repository.
+
+## [Code of conduct][code-of-conduct]
+
+We follow [Contributor Covenant Code of Conduct][code-of-conduct] in the all of repositories managed by [marp-team].
+
+## Question
+
+Keep in mind that **GitHub issue tracker is not a support forum.** _You should not expect answer to such a question at GitHub._
+
+You can use [StackOverflow](https://stackoverflow.com/) if you want.
+
+## Report issue
+
+At first, you should search similar issues before reporting your issue. It may have already been discussed or resolved in the other issue.
+
+[:mag: `org:marp-team is:issue [keyword]`](https://github.com/search?q=org%3Amarp-team+is%3Aissue+%5Bkeyword%5D) is useful to search issue from across our projects.
+
+<!-- TODO: Add guideline of the content of issue -->
+
+> :information_source: Several project is consisted by multiple packages created by [marp-team]. If you know which project causes an issue, please report issue to that repo.
+
+## Feature requests
+
+- Feature request gives feedback to our, but _it would not always implement_.
+- Each our packages always have just one core feature. The requested feature could be rejected if it's far from supporting the project core.
+- When there is a pull request implemented the brand new feature, the maintainer have to be careful to merge only the truly valuable features for project. If not, it just would trigger a scope creep.
+
+## Pull request
+
+<!-- TODO: Add guideline of the pull request -->
+
+[code-of-conduct]: https://github.com/marp-team/marp/blob/master/.github/CODE_OF_CONDUCT.md
+[marp-team]: https://github.com/marp-team/