Include plugin class docstring in the online docs

[psss]

Let's allow providing an introduction text for each step plugin class so that general information can be included in the online documentation.

Plus, specifically for the provision step, let's make the hardware specification more discoverable. Also include a simple example at the very beginning of the hardware.

Pull Request Checklist

• [ ] implement the feature
• [ ] write the documentation
• [ ] extend the test coverage
• [ ] update the specification
• [ ] adjust plugin docstring
• [ ] modify the json schema
• [ ] mention the version
• [ ] include a release note

[psss]

@bgoncalv, this should hopefully improve a little it your use case of searching for the hardware spec from provision plugin docs. Or do you think the link to the hardware should be rather provided in each and every plugin doc?

[bgoncalv]

@bgoncalv, this should hopefully improve a little it your use case of searching for the hardware spec from provision plugin docs. Or do you think the link to the hardware should be rather provided in each and every plugin doc?

I this should help as the provision section will mention the hardware section.

Btw, thanks for looking at this 😄