docs: update readme to include bun install (#182)

* docs: update readme to include bun install

* docs: update to include pnpm + bun

Author: Electroid

README.md

@@ -8,12 +8,14 @@ This repository contains the legacy ESLintRC configuration file format for ESLin
 
 You can install the package as follows:
 
-```
-npm install @eslint/eslintrc --save-dev
-
+```shell
+npm install @eslint/eslintrc -D
 # or
-
 yarn add @eslint/eslintrc -D
+# or
+pnpm install @eslint/eslintrc -D
+# or
+bun install @eslint/eslintrc -D
 ```
 
 ## Usage (ESM)