add link to the OTA docs in the README.md

Author: Links2004

README.md

@@ -50,6 +50,7 @@ Documentation for latest development version:
 - [Reference](doc/reference.md)
 - [Supported boards](doc/boards.md)
 - [Change log](doc/changes.md)
+- [OTA Update](doc/ota_updates.md)
 
 ### Issues and support ###