chore: add contributing and code of conduct

• Adapt a code of conduct from Contributor Covenant Code of Conduct
• Adapt a contribution guideline from Good-CONTRIBUTING.md-template.md.

CODE_OF_CONDUCT.md

+# 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, gender identity and expression, level of experience,
+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 at [yuji.isobe@emin.co.jp](mailto:yuji.isobe@emin.co.jp). 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 [http://contributor-covenant.org/version/1/4][version]
+
+[homepage]: http://contributor-covenant.org
+[version]: http://contributor-covenant.org/version/1/4/

CONTRIBUTING.md

+# Contributing
+
+First of all, thank you for your interest in contributing to headless-chrome-crawler!
+When contributing to this project, please first discuss the change you wish to make via issue before making a change.
+
+Please note that this project has a [code of conduct](https://github.com/yujiosaka/headless-chrome-crawler/blob/master/CODE_OF_CONDUCT.md), please follow it in all your interactions with this project.
+
+## Contributing Process
+
+1. Modify code following [ESLint](https://eslint.org) and the code should be annotated with [closure annotations](https://github.com/google/closure-compiler/wiki/Annotating-JavaScript-for-the-Closure-Compiler).
+2. Make sure all tests are passed by `yarn test`. Modify tests when the interface has changed.
+2. Update the [README.md](https://github.com/yujiosaka/headless-chrome-crawler/blob/master/README.md) with details of changes to the interface.
+3. Update the [CHANGELOG.md](https://github.com/yujiosaka/headless-chrome-crawler/blob/master/CHANGELOG.md). The versioning scheme we use is [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
+4. Make your commit message following [Conventional Commits](https://conventionalcommits.org/).
+5. Make a Pull Request and you may request a reviewer to merge your commit.