Participants don't know how to pass data to macros in task 3's stretch task

[36degrees]

This issue was observed whilst facilitating Prototype Kit training in Manchester on 20 February 2020.

The task 3 stretch task (using Nunjucks macros) does not tell the user how to pass the answer the answer gave to the macro (i.e. the use of value: data['foo'])

We had lots of participants asking how to do this when we reached this step.

prototype-kit-training/source/task3/task3.md

Lines 12 to 18 in 5db3119

	### Use some nunjucks macros in your prototype
	In task 2 you added some questions to your pages. To do that you copied and pasted HTML code from the [GOV.UK Design System](https://design-system.service.gov.uk/).
	Now we've talked a bit about Nunjucks macros, try replacing some HTML elements with the equivalent Nunjucks code.
	A good place to start would be the radio buttons on your `juggling-balls.html` page.