Creating an extensible Nintex Workflow add-on for SP 2013 On-premise

I have a strange technical requirement of a workflow that needs to execute a PowerShell command on the server side. I understand that this could be achieved via CSCRIPT in a C# code, but I'd rather create a solution that adds extensions (such as this PowerShell example) to the SharePoint Farm that can be leveraged by Nintex Workflow. Since my client is using Nintex, I'd rather not introduce any complexities and rather create a custom workflow action that appears in Nintex.

I've never worked in the API. Can I extend Nintex Workflow for 2013 as I described above? Is there documentation for this? All I have seen is documentation for 2010. My target platform is SP 2013 Server on-premise.

Thanks!