docs: improve documentation

Signed-off-by: Bart Jaskulski <bjaskulski@protonmail.com>

README.md

@@ -41,7 +41,13 @@ most of the time you will need a few more steps to make the most of plugin initi
 #### Using dependency injection container
 
 Paired with `php-di/php-di`, you are able to take leverage of dependency injection in your 
-WordPress plugin.
+WordPress plugin. `wp-init` is ready to pick up all of your hook provider classes from special 
+container entry named `hooks`. Any class registered in this array will be called during 
+`plugins_loaded` hook.
+
+```shell
+composer require php-di/php-di
+```
 
 ```php
 <?php
@@ -54,7 +60,11 @@ use WPDesk\Init\PluginInit;
 require __DIR__ . '/vendor/autoload.php';
 
 $plugin = (new PluginInit())
-    ->add_container_definitions(__DIR__ . '/config/services.inc.php')
+    ->add_container_definitions([
+        'hooks' => [
+            \DI\autowire( \Example\PostType\BookPostType::class )
+        ]
+    ])
     ->init();
 ```
 

src/PluginInit.php

@@ -24,6 +24,14 @@ final class PluginInit {
 	/** @var string|null Plugin identifier. */
 	private $slug;
 
+	/**
+	 * Define environment constraints required by a plugin. If requirements are not fulfilled,
+	 * the plugin will not be able to instantiate.
+	 *
+	 * Validation rules are defined according to `wp-basic-requirements` documentation.
+	 *
+	 * @see https://gitlab.wpdesk.dev/wpdesk/wp-basic-requirements
+	 */
 	public function set_requirements( array $requirements ): self {
 		$this->requirements = $requirements;