Add usage information

README.md

@@ -11,6 +11,40 @@ This yocLibrary enables your project to send and receive with EPP (Extensible Pr
 
 `composer require yocto/yoclib-epp`
 
-## Use
+## Usage
 
-*TODO*
+### Serializing
+
+```php
+use YOCLIB\EPP\EPPDocumentHelper;
+
+$doc = EPPDocumentHelper::createEPPDocument();
+
+$epp = $doc->createElementNS('urn:ietf:params:xml:ns:epp-1.0','epp');
+
+$hello = $doc->createElementNS('urn:ietf:params:xml:ns:epp-1.0','hello');
+
+$epp->appendChild($hello);
+
+$doc->appendChild($epp);
+
+$xml = $doc->saveXML();
+```
+
+### Deserializing
+
+```php
+use YOCLIB\EPP\EPPDocumentHelper;
+use YOCLIB\EPP\Elements\EPPEppElement;
+
+$xml = '<?xml version="1.0" encoding="UTF-8" standalone="no"?><epp xmlns="urn:ietf:params:xml:ns:epp-1.0"><hello/></epp>';
+
+$doc = EPPDocumentHelper::createEPPDocument();
+
+$doc->loadXML($xml);
+
+/**@var EPPEppElement $epp*/
+$epp = $doc->documentElement;
+
+$hello = $epp->getHello();
+```