[Docs] Add guide for rest resource generation

REST_RESOURCE.md

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+# Adding a New API Version to Shopify API PHP
+
+## Overview
+This guide provides step-by-step instructions for adding a new API version to the Shopify API PHP library. This example uses the addition of the 2025-07 API version as a reference, but the process applies to any new API version.
+
+## Prerequisites
+- Understanding of any breaking changes or removed resources in the new API version
+
+## Step 1: Update API Version Constants
+
+### Add New Version Constant
+Edit `src/ApiVersion.php` to add your new version:
+
+```php
+// Add the new constant following the naming pattern
+public const JULY_2025 = "2025-07";  // Replace with your version
+
+// If this is the latest version, update the LATEST constant
+public const LATEST = self::JULY_2025;  // Update from previous latest
+```
+
+**Naming Convention:**
+- Format: `{MONTH}_{YEAR}`
+- Examples: `APRIL_2025`, `JULY_2025`, `OCTOBER_2025`
+
+## Step 2: Create Directory Structure
+
+### Create Source Directory
+```bash
+mkdir src/Rest/Admin{YYYY_MM}/
+```
+Example: `src/Rest/Admin2025_07/`
+
+### Create Test Directory
+```bash
+mkdir tests/Rest/Admin{YYYY_MM}/
+```
+Example: `tests/Rest/Admin2025_07/`
+
+## Step 3: Copy and Update Resource Files
+
+### Copy Previous Version's Files
+Copy all files from the most recent API version directory:
+
+```bash
+# Copy source files
+cp -r src/Rest/Admin{PREVIOUS_VERSION}/* src/Rest/Admin{NEW_VERSION}/
+
+# Copy test files  
+cp -r tests/Rest/Admin{PREVIOUS_VERSION}/* tests/Rest/Admin{NEW_VERSION}/
+```
+
+### Update Each Resource File
+For each PHP file in the new directory, update:
+
+1. **Namespace**
+   ```php
+   // From
+   namespace Shopify\Rest\Admin{PREVIOUS_VERSION};
+
+   // To
+   namespace Shopify\Rest\Admin{NEW_VERSION};
+   ```
+
+2. **API Version String**
+   ```php
+   // From
+   public static string $API_VERSION = "{PREVIOUS_VERSION}";
+
+   // To
+   public static string $API_VERSION = "{NEW_VERSION}";
+   ```
+
+### Example Resource File Update
+
+**Before (Admin2025_04/Article.php)**:
+```php
+namespace Shopify\Rest\Admin2025_04;
+
+use Shopify\Auth\Session;
+use Shopify\Rest\Base;
+
+class Article extends Base
+{
+    public static string $API_VERSION = "2025-04";
+    // ... rest of the file is identical
+}
+```
+
+**After (Admin2025_07/Article.php)**:
+```php
+namespace Shopify\Rest\Admin2025_07;
+
+use Shopify\Auth\Session;
+use Shopify\Rest\Base;
+
+class Article extends Base
+{
+    public static string $API_VERSION = "2025-07";
+    // ... rest of the file is identical
+}
+```
+
+## Step 4: Update Test Files
+
+### Rename Test Files
+Update the naming convention for test files:
+```
+{ResourceName}{YYYYMM}Test.php
+```
+Example: `Article202504Test.php` → `Article202507Test.php`
+
+### Update Test File Contents
+For each test file, update:
+
+1. **Use Statement**
+   ```php
+   // From
+   use Shopify\Rest\Admin{PREVIOUS_VERSION}\Article;
+
+   // To
+   use Shopify\Rest\Admin{NEW_VERSION}\Article;
+   ```
+
+2. **Context API Version**
+   ```php
+   // From
+   Context::$API_VERSION = "{PREVIOUS_VERSION}";
+
+   // To
+   Context::$API_VERSION = "{NEW_VERSION}";
+   ```
+
+3. **URL Paths in Mock Requests**
+   ```php
+   // From
+   "https://test-shop.myshopify.io/admin/api/{PREVIOUS_VERSION}/..."
+
+   // To
+   "https://test-shop.myshopify.io/admin/api/{NEW_VERSION}/..."
+   ```
+
+## Step 5: Handle Breaking Changes
+
+### Identify Removed or Modified Resources
+Check the Shopify API changelog for:
+- Removed resources (e.g., CustomerAddress in 2025-07)
+- Modified endpoints
+- Changed field names or types
+
+### Remove Deprecated Resources
+If a resource is removed in the new API version:
+1. Delete the resource file from `src/Rest/Admin{NEW_VERSION}/`
+2. Delete the corresponding test file from `tests/Rest/Admin{NEW_VERSION}/`
+
+### Update Modified Resources
+If a resource has changed:
+1. Update the resource class properties
+2. Modify the `$PATHS` array if endpoints changed
+3. Update method signatures if parameters changed
+4. Adjust test cases accordingly
+
+
+## Checklist
+
+- [ ] Added new version constant to `src/ApiVersion.php`
+- [ ] Updated `LATEST` constant if applicable
+- [ ] Created `src/Rest/Admin{NEW_VERSION}/` directory
+- [ ] Created `tests/Rest/Admin{NEW_VERSION}/` directory
+- [ ] Copied all resource files from previous version
+- [ ] Updated namespaces in all resource files
+- [ ] Updated API_VERSION in all resource files
+- [ ] Renamed all test files with new version suffix
+- [ ] Updated test file imports and contexts
+- [ ] Updated all API URLs in test mocks
+- [ ] Removed deprecated resources
+- [ ] Updated modified resources
+- [ ] Run all tests successfully