Add usage examples.

Author: sibprogrammer

README.md

@@ -10,6 +10,38 @@ PHP object-oriented library for Plesk XML-RPC API.
 
 `composer require plesk/api-php-lib:@dev`
 
+## Usage Examples
+
+Here is an example on how to use the library and create a customer with desired properties:
+```php
+$client = new \PleskX\Api\Client($host);
+$client->setCredentials($login, $password);
+
+$client->customer()->create([
+    'cname' => 'Plesk',
+    'pname' => 'John Smith',
+    'login' => 'john',
+    'passwd' => 'secret',
+    'email' => '[email protected]',
+]);
+```
+
+It is possible to use a secret key instead of password for authentication.
+
+```php
+$client = new \PleskX\Api\Client($host);
+$client->setSecretKey($secretKey)
+```
+
+In case of Plesk extension creation one can use an internal mechanism to access XML-RPC API. It does not require to pass authentication because the extension works in the context of Plesk.
+
+```php
+$client = new \PleskX\Api\InternalClient();
+$protocols = $client->server()->getProtos();
+```
+
+For additional examples see tests/ directory.
+
 ## How to Run Unit Tests
 
 One the possible ways to become familiar with the library is to check the unit tests.
@@ -27,4 +59,3 @@ To use custom port one can provide a URL (e.g. for Docker container):
 * Install Node.js
 * Install dependencies via `npm install` command
 * Run `REMOTE_HOST=your-plesk-host.dom REMOTE_PASSWORD=password grunt watch:test`
-