Add install docs

README.md

@@ -3,3 +3,29 @@
 [![changesets](https://img.shields.io/badge/maintained%20with-changesets-blue)](https://github.com/atlassian/changesets)
 
 Widen's shared ESLint config and plugins.
+
+## Installation
+
+```sh
+yarn add -D eslint eslint-{config,plugin}-widen eslint-plugin-sort @babel/{core,eslint-parser}
+
+# If you use TypeScript
+yarn add -D @typescript-eslint/{eslint-plugin,parser}
+
+# If you use React
+yarn add -D eslint-plugin-{react,react-hooks,jsx-a11y}
+
+# If you use Jest
+yarn add -D eslint-plugin-jest
+```
+
+## Usage
+
+In your `.eslintrc` file, add the following four entries to your extends list.
+If you don't need a specific configuration, simply remove it from the list.
+
+```json
+{
+  "extends": ["widen", "widen/typescript", "widen/react", "widen/jest"]
+}
+```