Add ESLint rule for React Hooks

Author: calebmer

packages/eslint-plugin-react-hooks/README.md

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+# `eslint-plugin-react-hooks`
+
+This ESLint plugin enforces the [Rules of Hooks](https://reactjs.org/docs/hooks-rules.html).
+
+It is a part of the [Hooks proposal](https://reactjs.org/docs/hooks-intro.html) for React.
+
+## Experimental Status
+
+This is an experimental release and is intended to be used for testing the Hooks proposal with React 16.7 alpha. The exact heuristics it uses may be adjusted.
+
+The [Rules of Hooks](https://reactjs.org/docs/hooks-rules.html) documentation contains a link to the technical RFC. Please leave a comment on the RFC if you have concerns or ideas about how this plugin should work.
+
+## Installation
+
+**Note: If you're using Create React App, please wait for a corresponding experimental release of `react-scripts` that includes this rule instead of adding it directly.**
+
+Assuming you already have ESLint installed, run:
+
+```sh
+# npm
+npm install eslint-plugin-react-hooks@next --save-dev
+
+# yarn
+yarn add eslint-plugin-react-hooks@next --dev
+```
+
+Then add it to your ESLint configuration:
+
+```js
+{
+  "plugins": [
+    // ...
+    "react-hooks"
+  ],
+  "rules": {
+    // ...
+    "react-hooks/rules-of-hooks": "error"
+  }
+}
+```
+
+## Valid and Invalid Examples
+
+Please refer to the [Rules of Hooks](https://reactjs.org/docs/hooks-rules.html) documentation and the [Hooks FAQ](https://reactjs.org/docs/hooks-faq.html#what-exactly-do-the-lint-rules-enforce) to learn more about this rule.
+
+## License
+
+MIT