docs: add contributing guidelines

CONTRIBUTING.md

@@ -0,0 +1,87 @@
+# Contributing
+
+Thanks for being willing to contribute!
+
+Working on your first Pull Request? You can learn how from this free series
+[How to Contribute to an Open Source Project on GitHub](https://egghead.io/series/how-to-contribute-to-an-open-source-project-on-github).
+
+## Project setup
+
+1. Fork this repository
+2. Clone your forked repository
+3. Run `npm install` to install corresponding dependencies
+4. Create a branch for your PR named like `pr/your-branch-name` (you can do this through git CLI with `git checkout -b pr/your-branch-name`)
+
+> Tip: Keep your `master` branch pointing at the original repository and make
+> pull requests from branches on your fork. To do this, run:
+>
+> ```
+> git remote add upstream https://github.com/testing-library/eslint-plugin-testing-library.git
+> git fetch upstream
+> git branch --set-upstream-to=upstream/master master
+> ```
+>
+> This will add the original repository as a "remote" called "upstream," Then
+> fetch the git information from that remote, then set your local `master`
+> branch to use the upstream master branch whenever you run `git pull`. Then you
+> can make all of your pull request branches based on this `master` branch.
+> Whenever you want to update your version of `master`, do a regular `git pull`.
+
+## Committing and Pushing changes
+
+Git hooks are configured on this project when you install dependencies.
+The following will be run on every commit:
+
+- Lint and format files automatically
+- Check all tests are passing
+- Check commit message is following [Conventional Commit specification](https://www.conventionalcommits.org/en/v1.0.0/)
+
+If you ever need to update a snapshot, you can run `npm run test:update`
+
+## Rule naming conventions
+
+Based on [ESLint's Rule Naming Conventions](https://eslint.org/docs/developer-guide/working-with-rules#rule-naming-conventions), you must follow these rules:
+
+- If your rule is disallowing something, prefix it with `no-` such as `no-debug`
+  for disallowing `debug()`.
+- If your rule is suggesting to prefer a way of doing something, among other ways, you can **optionally** prefix it with
+  `prefer-`. For example, `prefer-screen-queries` suggests to use `screen.getByText()` from imported `screen` rather
+  than `getByText()` from `render`'s result though both are technically fine.
+- If your rule is enforcing the inclusion of something, use a short name without a special prefix. As an example,
+  `await-async-utils` enforce to wait for proper async utils.
+- Use dashes between words.
+- Try to keep the name simple and clear.
+
+## Adding new rules
+
+In the [same way as ESLint](https://eslint.org/docs/developer-guide/working-with-rules),
+each rule has three files named with its identifier (e.g. `no-debug`):
+
+- in the `lib/rules` directory: a source file (e.g. `no-debug.js`)
+- in the `tests/lib/rules` directory: a test file (e.g. `no-debug.js`)
+- in the `docs/rules` directory: a Markdown documentation file (e.g. `no-debug.md`)
+
+Additionally, you need to do a couple of extra things:
+
+- Import the new rule in `lib/index.js` and include it
+  in `rules` constant (there is a test which will make sure you did
+ this). Remember to include your rule under corresponding `config` if necessary
+  (a snapshot test will check this too, but you can update it just running
+  `npm run test:update`).
+- Include your rule in the "Supported Rules" table within the [README.md](./README.md).
+  Don't forget to include the proper badges if needed and to sort alphabetically the rules for readability.
+
+## Modifying rules
+
+A couple of things you need to remember when editing already existing rules:
+
+- If renaming a rule, make sure to update all points mentioned in
+  "Adding new rules" section.
+- Try to add tests to cover the changes introduced, no matter if that's
+  a bug fix or a new feature.
+
+## Help needed
+
+Please check the [the open issues](https://github.com/testing-library/eslint-plugin-testing-library/issues)
+
+Also, please watch the repo and respond to questions/bug reports/feature requests! Thanks!

package.json

@@ -30,6 +30,7 @@
     "format": "prettier --write README.md {lib,docs,tests}/**/*.{js,md}",
     "test:local": "jest",
     "test:ci": "jest --coverage",
+    "test:update": "npm run test:local -- --u",
     "test:watch": "npm run test:local -- --watch",
     "test": "is-ci test:ci test:local",
     "semantic-release": "semantic-release"