docs: update ESLint package docs (#9833)

### Description

Copies the READMEs of the packages up into docs.

In the future, we should find a way to automate this (or stub the npm
doc to point at our docs).

### Testing Instructions

👀

Author: anthonyshew

docs/repo-docs/reference/eslint-config-turbo.mdx

@@ -35,12 +35,60 @@ Install `eslint-config-turbo` into the location where your ESLint configuration
   </Tab>
 </PackageManagerTabs>
 
-## Usage
+## Usage (Flat Config `eslint.config.js`)
 
-In your ESLint configuration file, add the package:
+```js title="./packages/eslint-config/base.js"
+import turboConfig from 'eslint-config-turbo/flat';
 
-```json title="./packages/config-eslint/index.js"
+export default [
+  ...turboConfig,
+  // Other configuration
+];
+```
+
+You can also configure rules available in the configuration:
+
+```js title="./packages/eslint-config/base.js"
+import turboConfig from 'eslint-config-turbo/flat';
+
+export default [
+  ...turboConfig,
+  // Other configuration
+  {
+    rules: {
+      'turbo/no-undeclared-env-vars': [
+        'error',
+        {
+          allowList: ['^ENV_[A-Z]+$'],
+        },
+      ],
+    },
+  },
+];
+```
+
+## Usage (Legacy `eslintrc*`)
+
+Add `turbo` to the extends section of your eslint configuration file. You can omit the `eslint-config-` prefix:
+
+```json title="./packages/eslint-config/base.json"
 {
   "extends": ["turbo"]
 }
 ```
+
+You can also configure rules available in the configuration:
+
+```json title="./packages/eslint-config/base.json"
+{
+  "plugins": ["turbo"],
+  "rules": {
+    "turbo/no-undeclared-env-vars": [
+      "error",
+      {
+        "allowList": ["^ENV_[A-Z]+$"]
+      }
+    ]
+  }
+}
+```

docs/repo-docs/reference/eslint-plugin-turbo.mdx

@@ -0,0 +1,121 @@
+---
+title: eslint-plugin-turbo
+description: Learn more about eslint-plugin-turbo.
+---
+
+import { PackageManagerTabs, Tab } from '#/components/tabs';
+
+[The `eslint-plugin-turbo` package](https://www.npmjs.com/package/eslint-plugin-turbo) helps you find environment variables that are used in your code that are not a part of Turborepo's hashing. Environment variables used in your source code that are not accounted for in `turbo.json` will be highlighted in your editor and errors will show as ESLint output.
+
+## Installation
+
+Install `eslint-config-turbo` into the location where your ESLint configuration is held:
+
+<PackageManagerTabs>
+  <Tab>
+
+    ```bash title="Terminal"
+    npm i --save-dev eslint-config-turbo -w @acme/eslint-config
+    ```
+
+  </Tab>
+  <Tab>
+
+    ```bash title="Terminal"
+    yarn workspace @acme/eslint-config add eslint-config-turbo --dev
+    ```
+
+  </Tab>
+  <Tab>
+
+    ```bash title="Terminal"
+    pnpm add eslint-config-turbo --filter=@repo/eslint-config
+    ```
+
+  </Tab>
+</PackageManagerTabs>
+
+## Usage (Flat Config `eslint.config.js`)
+
+ESLint v9 uses the Flat Config format seen below:
+
+```js title="./packages/eslint-config/base.js"
+import turbo from 'eslint-plugin-turbo';
+
+export default [turbo.configs['flat/recommended']];
+```
+
+Otherwise, you may configure the rules you want to use under the rules section.
+
+```js title="./packages/eslint-config/base.js"
+import turbo from 'eslint-plugin-turbo';
+
+export default [
+  {
+    plugins: {
+      turbo,
+    },
+    rules: {
+      'turbo/no-undeclared-env-vars': 'error',
+    },
+  },
+];
+```
+
+## Example (Flat Config `eslint.config.js`)
+
+```js title="./packages/eslint-config/base.js"
+import turbo from 'eslint-plugin-turbo';
+
+export default [
+  {
+    plugins: {
+      turbo,
+    },
+    rules: {
+      'turbo/no-undeclared-env-vars': [
+        'error',
+        {
+          allowList: ['^ENV_[A-Z]+$'],
+        },
+      ],
+    },
+  },
+];
+```
+
+## Usage (Legacy `eslintrc*`)
+
+Add `turbo` to the plugins section of your `.eslintrc` configuration file. You can omit the `eslint-plugin-` prefix:
+
+```json title="./packages/eslint-config/base.json"
+{
+  "plugins": ["turbo"]
+}
+```
+
+Then configure the rules you want to use under the rules section.
+
+```json title="./packages/eslint-config/base.json"
+{
+  "rules": {
+    "turbo/no-undeclared-env-vars": "error"
+  }
+}
+```
+
+## Example (Legacy `eslintrc*`)
+
+```json title="./packages/eslint-config/base.json"
+{
+  "plugins": ["turbo"],
+  "rules": {
+    "turbo/no-undeclared-env-vars": [
+      "error",
+      {
+        "allowList": ["^ENV_[A-Z]+$"]
+      }
+    ]
+  }
+}
+```

docs/repo-docs/reference/meta.json

@@ -25,6 +25,7 @@
     "---Packages---",
     "create-turbo",
     "eslint-config-turbo",
+    "eslint-plugin-turbo",
     "turbo-ignore",
     "turbo-codemod",
     "turbo-gen"