Add MTA spec v3 in README (#1145)

Author: boyan-velinov

README.md

@@ -17,7 +17,7 @@
 
 #### Multi-Target Application
 
-Before using this package, make sure that you are familiar with the multi-target application concept and terminology. For background and detailed information, see the [Multi-Target Application Model](https://www.sap.com/documents/2016/06/e2f618e4-757c-0010-82c7-eda71af511fa.html) guide. 
+Before using this package, make sure that you are familiar with the multi-target application concept and terminology. For background and detailed information, see the [Multi-Target Application Model v.2](https://www.sap.com/documents/2016/06/e2f618e4-757c-0010-82c7-eda71af511fa.html) or [Multi-Target Application Model v.3](https://www.sap.com/documents/2021/09/66d96898-fa7d-0010-bca6-c68f7e60039b.html) . 
 
 #### The Cloud MTA Build Tool Overview
 The Cloud MTA Build Tool is a standalone command-line tool that builds a deployment-ready