add info aboun api v2/v3 in README.md

Author: Piotr Suszalski

README.md

@@ -2,6 +2,15 @@
 
 A php library which implements the functionality of FreshMail REST API.
 
+This API client covers all functions of API V2 such as:
+ - subscribers management
+ - list management
+ - campaign management
+ - sending transactional SMS messages
+ - sending transactional mail messages (in a legacy way)
+
+If You want to send transactional messages in rich format please use new [API V3 client](https://github.com/FreshMail/php-api-client).
+
 ## Installation via composer
 
 Add to `composer.json` file:
@@ -26,4 +35,4 @@ Use in php project:
 All samples included in samples directory.
 
 ## Thanks to
-@adam187 
+@adam187