docs(readme): add readme

Author: fadrian06

README.md

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+# FlightPHP Container
+
+A lightweight Dependency Injection Container (DIC) for PHP, to manage and streamline object dependencies effectively.
+
+## Features
+
+- **Lightweight and Efficient:** Manage dependencies with ease.
+- **Flexible Configuration:** Easily integrate with various PHP applications.
+- **PSR-11 Compliance:** Ensures interoperability between containers.
+
+## Requirements
+
+- PHP 7.4 or higher
+- Composer installed on your system
+
+## Installation
+
+To include the FlightPHP Container in your project, you can use Composer:
+
+```bash
+composer require flightphp/container
+```
+
+## Simple usage
+
+To use the FlightPHP Container, you can create a new instance of the container and bind your dependencies:
+
+```php
+<?php
+
+require 'vendor/autoload.php';
+
+use Flight\Container;
+
+$container = new Container;
+
+$container->set(PDO::class, fn(): PDO => new PDO(
+  'mysql:host=localhost;dbname',
+  'username',
+  'password'
+));
+
+$pdo = $container->get(PDO::class);
+
+var_dump($pdo);
+
+/*
+object(PDO)#3 (0) {
+}
+ */
+```
+
+## Usage in FlightPHP Framework
+
+You can use the FlightPHP Container in your FlightPHP application by setting the container instance:
+
+```php
+<?php
+
+require 'vendor/autoload.php';
+
+use Flight\Container;
+
+$container = new Container;
+
+$container->set(PDO::class, fn(): PDO => new PDO(
+  'mysql:host=localhost;dbname',
+  'username',
+  'password'
+));
+
+Flight::registerContainerHandler($container);
+
+class TestController {
+  function __construct(private PDO $pdo) {}
+
+  function index() {
+    var_dump($this->pdo);
+  }
+}
+
+Flight::route('GET /', [TestController::class, 'index']);
+
+Flight::start();
+```
+
+Go and visit that route in your dev server and you'll see something like:
+
+```
+object(PDO)#3 (0) {
+}
+```
+
+## Advance usage
+
+FlightPHP Container can resolve dependencies recursively, allowing you to bind complex objects and dependencies:
+
+```php
+<?php
+
+require 'vendor/autoload.php';
+
+use Flight\Container;
+
+class User {}
+
+interface UserRepository {
+  function find(int $id): ?User;
+}
+
+class PdoUserRepository implements UserRepository {
+  private PDO $pdo;
+
+  function __construct(PDO $pdo) {
+    $this->pdo = $pdo;
+  }
+
+  function find(int $id): ?User {
+    // Implementation ...
+  }
+}
+
+$container = new Container;
+
+$container->set(PDO::class, static fn(): PDO => new PDO(
+  'mysql:host=localhost;dbname=test',
+  'username',
+  'password'
+));
+
+$container->set(UserRepository::class, PdoUserRepository::class);
+
+$userRepository = $container->get(UserRepository::class);
+
+var_dump($userRepository);
+
+/*
+object(PdoUserRepository)#4 (1) {
+  ["pdo":"PdoUserRepository":private]=>
+  object(PDO)#3 (0) {
+  }
+}
+ */
+```
+
+## License
+
+FlightPHP Container is open-sourced software licensed under the [MIT license](https://opensource.org/licenses/MIT).