Hello Thulasi Pasam,
as far as I know, there are no documents about product upgrade / migration for Nintex Workflow / Forms for SharePoint 2016 available, yet.
However, you can use the "Follow" function with "Inbox" ticked to receive updates for the following pages. I suppose Nintex will list the documents there as soon es they become available:
You should also have a look at ShareGate. (Nintex and Sharegate Announce Partnership to Move Customers to Office 365) - You can already use their tool to move workflows to Office 365. It might also become handy for migration from SP2013 to SP2016.
We are working on 2016 versions of our products. At this stage, I'm not in a position to comment more on the details about the products or release dates.
Are there specific features you are looking for though?