doc: Update CONTRIBUTING.md

Author: thefeqy

CONTRIBUTING.md

@@ -1,11 +1,11 @@
-# 🛠 Contributing to Grok PHP Client
+# Contributing to Grok PHP Client
 
-Thank you for your interest in contributing to **Grok PHP Client**! 🚀  
+Thank you for your interest in contributing to **Grok PHP Client**!  
 We appreciate your help in improving the package. Whether you're fixing bugs, adding new features, or improving documentation—your contributions make a difference!
 
 ---
 
-## **📌 How to Contribute**
+## **How to Contribute**
 ### **1️⃣ Fork the Repository**
 Click the **"Fork"** button at the top-right of the [repository](https://github.com/grok-php/client).
 
@@ -28,7 +28,7 @@ To confirm everything works before adding new changes:
 ```sh
 composer test
 or
-vendor/bin/pest
+vendor/bin/phpunit
 ```
 
 ### 5️⃣ Create a New Branch
@@ -58,39 +58,59 @@ git push origin feature/your-new-feature
 
 ### 9️⃣ Open a Pull Request (PR)
 Go to [Grok PHP Client Repo](https://github.com/grok-php/client/pulls)
-Click "New Pull Request", select your branch, and submit 🚀
+Click "New Pull Request", select your branch, and submit 
 
 ---
 
-## 🧪 Running Tests
-We use Pest PHP for testing. Before submitting your PR, run:
+## Running Tests
+1. To run **PHPUnit**, you should copy the `phpunit.xml.dist` file to `phpunit.xml`.
 
+```sh
+cp phpunit.xml.dist phpunit.xml
+```
+
+2. **Update** the API key in `phpunit.xml` with your actual API key:
+```xml
+<php>
+    <env name="GROK_API_KEY" value="your-grok-api-key-here"/>
+</php>
+```
+3. **Obtain an API Key:**  
+   If you don’t have an API key, sign up at [Grok AI](https://x.ai/api/) and create one.
+
+4. **Run the tests with PHPUnit:**
 ```sh
 composer test
-or
-vendor/bin/pest
+```
+Or run **PHPUnit** manually:
+```sh
+vendor/bin/phpunit
 ```
 
 ✅ If all tests pass, your PR is good to go!
+
 ❌ If tests fail, debug the issue before pushing changes.
 
 ---
 
-## 📖 Coding Guidelines
+## Coding Guidelines
 ✔️ Follow PSR-12 Standards
+
 ✔️ Use PHP 8.1+ Features (typed properties, enums, readonly properties)
+
 ✔️ Document Code Clearly (use PHPDoc annotations)
+
 ✔️ Write Meaningful Commit Messages
 
 ---
 
-## 🔒 Security Policy
+## Security Policy
 If you discover a security vulnerability, please do NOT open a public issue. Instead, report it privately via email:
 📩 [thefeqy@gmail.com](thefeqy@gmail.com)
 
 ---
 
-## 💡 Feature Requests & Discussions
+## Feature Requests & Discussions
 Open an issue in [GitHub Issues](https://github.com/grok-php/client/issues)
 Share ideas on new ***features, optimizations, or improvements***.