added instruction of installation into README

README.md

@@ -2,6 +2,44 @@
 
 A set of tools to simplify the work of creating backend APIs for your frontend projects. Includes tutorials, patterns and practical examples for creating projects based on REST APIs.
 
+## Installation
+
+Download source code and add to your project
+
+```php
+<?php
+require_once __DIR__ . '/APIlite/src/APIlite.php';
+```
+
+or use composer
+
+```bash
+composer require tpsoft/apilite
+```
+
+and add to your project
+
+```php
+<?php
+require __DIR__ . '/vendor/autoload.php';
+
+class YourAPI extends \TPsoft\APIlite\APIlite {
+
+	/**
+	 * My first method for greetings.
+	 *
+	 * @param string $name Your name
+	 * @param int $age Your age
+	 * @return string Greetings
+	 */
+	public function myFirstMethod(string $name, int $age): string
+	{
+		return 'Hi, I`m '.$name.' and I`m '.$age.' years old.';
+	}
+
+}
+```
+
 ## Basic usage
 
 For example, we create an API for calculator. So we create class `APIcalculator` and store in file `test/APIcalculator.php` where we defined each actions for API as public method.