docs: Add brief ESLint instructions

Author: lachlancollins

docs/eslint.md

@@ -3,4 +3,22 @@ id: eslint
 title: ESLint
 ---
 
-To-do!
+## Setup
+
+### package.json
+
+- Make sure you have ESLint v8.57.0+ installed
+- We will upgrade to ESLint v9 once `typescript-eslint` v8 and `eslint-plugin-react-hooks` v5 release
+
+### eslint.config.js
+
+```js
+import { rootConfig } from '@tanstack/config/eslint'
+
+export default [
+  ...rootConfig,
+  {
+    // Custom rules go here
+  },
+]
+```