What I have done is used snagit to take screenshots and then paste it into a word document. With snag it you can crop and add call outs or arrows to the screenshot using the snag it tools. Next to the screen shot you could possibly add a few bullet points on what the actions are doing. I attached a sample screenshot of what I have in my workflow document. I hope it helps.
Great suggestions so far, and I would say that the documentation that I've had to write depends greatly on the complexity of the workflow, as well as what would help the customer best understand the workflow/business process at hand. This often includes a mixture of text with screen shots captured of the most important parts of the workflow (or sometimes the parts least likely to be understood). You really can't go wrong as long as your documentation tells the story that is required to be told.
do you know the print functionality of Nintex Workflow.
There are 2 options. One is only print and one is called "print with notes".
When you configure an item, take the tab "labels" and in the section: "Notes to display", choose User defined and write your comment in this field.
When you print it, you can see your comments below the workflow.
With big workflows, you should split in Main- and subworkflows not only for readability.
When my audience is less technical I almost always use visio to document the process of the workflow.
Visio also helps when designing a workflow before build with technical teams as well. Then once it is built we can review using the screen captures or print outs of the workflow itself from the Nintex Designer with notes.
Many times I use Excel to supplement some areas that need to be documented. Such as notifications and tasks. With Excel we will map out the different components of the notifications. Like Subject, Body, and assigned to. This is very useful when building a workflow that has many notifications. But may not be necessary for a simpler workflow.
Pairing up the opensource tool Greenshot with Workflow Analyzer is what I like to use for documentation/annotation of workflows.