chore(readme): more documentation

README.md

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+
+WP Builder
+==========
+
+wp-builder defines interfaces and abstracts to create WordPress plugins. 
+
+## Requirements
+
+PHP 5.6 or later.
+
+## Installation via Composer
+
+In order to install the bindings via [Composer](http://getcomposer.org/) run the following command:
+
+```bash
+composer require wpdesk/wp-builder
+```
+
+## Example usage
+
+Use this code in main WordPress plugin file:
+
+```php
+<?php
+
+class ContentExtender implements \WPDesk\PluginBuilder\Plugin\Hookable {
+
+	public function hooks() {
+		add_filter( 'the_content', [ $this, 'append_sample_text_to_content' ] );
+	}
+	
+	/**
+	 * @param string $content
+	 * @return string
+ 	 */
+	public function append_sample_text_to_content( $content ) {
+		return $content . ' Sample text';
+	}
+}
+
+class ExamplePlugin extends \WPDesk\PluginBuilder\Plugin\AbstractPlugin implements \WPDesk\PluginBuilder\Plugin\HookableCollection {
+
+	use \WPDesk\PluginBuilder\Plugin\HookableParent;
+	
+	public function hooks() {
+		$this->add_hookable( new ContentExtender() );
+		
+		$this->hooks_on_hookable_objects();
+	}
+
+}
+
+$plugin_info = new WPDesk_Plugin_Info();
+$plugin_info->set_plugin_name( 'Example Plugin' );
+
+$example_plugin = new ExamplePlugin( $plugin_info ); 
+
+```