chore: adds php ai client tool readme

Author: JasonTheAdams

tools/php-ai-client/README.md

@@ -0,0 +1,51 @@
+# PHP AI Client Installer
+
+Bundles the [wordpress/php-ai-client](https://github.com/WordPress/php-ai-client) library into WordPress Core at `src/wp-includes/php-ai-client/`.
+
+The installer fetches the package, scopes its third-party dependencies (Http\*, Psr\*, etc.) under `WordPress\AiClientDependencies\*` using [PHP-Scoper](https://github.com/humbug/php-scoper) to avoid conflicts with plugins, reorganizes the files into a namespace-based layout, and generates a manual autoloader.
+
+## Prerequisites
+
+- PHP
+- Composer
+- Git
+
+## Usage
+
+Run from the WordPress development repository root:
+
+```bash
+# Install a specific release version
+bash tools/php-ai-client/installer.sh --version=1.0.0
+
+# Install from a branch
+bash tools/php-ai-client/installer.sh --branch=main
+```
+
+You must specify either `--version` or `--branch` (not both).
+
+## What It Does
+
+1. Clones the package from GitHub (shallow clone of the specified ref).
+2. Runs `composer install --no-dev` to fetch dependencies.
+3. Downloads PHP-Scoper and scopes all dependency namespaces to `WordPress\AiClientDependencies\*`.
+4. Reorganizes scoped dependencies from Composer's `vendor/` layout into a namespace-based `third-party/` directory.
+5. Removes unused files (async/promise support, deprecated discovery classes, etc.).
+6. Generates `autoload.php` with a PSR-4 autoloader.
+7. Validates the output.
+
+## Output Structure
+
+```
+src/wp-includes/php-ai-client/
+├── autoload.php      # Generated autoloader
+├── src/              # AI Client source (WordPress\AiClient\*)
+└── third-party/      # Scoped dependencies (WordPress\AiClientDependencies\*)
+    ├── Http/
+    └── Psr/
+```
+
+## Support Files
+
+- **`scoper.inc.php`** — PHP-Scoper configuration. Defines the scoping prefix, excludes the AI Client's own namespace, and patches php-http/discovery to preserve references to external HTTP implementations.
+- **`reorganize.php`** — Reads Composer's `installed.json` and copies scoped vendor files into a flat namespace-based directory structure.