docs(contributing): add CONTRIBUTING.md

https://github.com/thoughtbot/factory_bot_rails/blob/master/CONTRIBUTING.md

Author: remarkablemark

CONTRIBUTING.md

@@ -0,0 +1,46 @@
+# Contributing
+
+All pull requests are welcome! By participating in this project, you
+agree to abide by our **[code of conduct]**.
+
+[code of conduct]: https://github.com/remarkablemark/html-react-parser/blob/master/CODE_OF_CONDUCT.md
+
+[Fork], then clone the repository:
+
+[fork]: https://github.com/remarkablemark/html-react-parser/fork
+
+```sh
+# replace `<user>` with your username
+$ git clone git@github.com:<user>/html-react-parser.git
+$ cd html-react-parser
+```
+
+Install package dependencies:
+
+```sh
+$ npm install
+```
+
+Make your change. Add tests and/or documentation. Ensure all tests and lint pass:
+
+```sh
+$ npm test
+$ npm run lint
+```
+
+Push to your fork and [submit a pull request][pr].
+
+[pr]: https://github.com/remarkablemark/html-react-parser/compare/
+
+At this point you're waiting on us. We like to comment on pull requests
+within three business days (and, typically, one business day). We may suggest
+changes, improvements, or alternatives.
+
+Things that will improve the chance that your pull request will be accepted:
+
+- [ ] Write tests that pass [CI].
+- [ ] Write good documentation.
+- [ ] Write a [good commit message][commit].
+
+[ci]: https://travis-ci.org/remarkablemark/html-react-parser
+[commit]: https://www.conventionalcommits.org/