Why are Jenkin's Plugins documentation so awful? JUnit is not an exception either!

### Describe your use-case which is not covered by existing documentation.

The frustrating part of the current documentation is there is zero discussion about Pipeline style properties. There are vague hints. But zero direct discussions about the available properties.

### Reference any relevant documentation, other materials or issues/pull requests that can be used for inspiration.

You have to guess the syntax from the documentation under **Configuration**. For example, the first entry is **Test report XMLs**. If you are using a **JenkinsFile** pipeline how do you configure the plugin? You'd have to guess `testResults` which shares NOTHING with **Test report XMLs**. Or what is the **Retain long standard output/error** property? Actually I have no idea. I'm pretty sure the slash can't be included. I even tried reading the Javadoc clicking through all of the classes and couldn't figure it out.

The only hint for the most important option is in an example way down the page under the git:

```
junit skipPublishingChecks: true, testResults: 'test-results.xml'
```

But no real discussion about it or if it even corresponds with the documentation above. You're just left to guess.

### Are you interested in contributing to the documentation?

Expectations:
* Document each option you can pass to the `junit` function. You could combine them with the `Configuration` documentation, or make it a separate section specifically for people using Pipeline syntax.
* Have some examples showing people how to use the options. Knowing the options is one thing, but the broader syntax of using those options is important. And it really helps new users just to see an example so they don't have to read your entire docs before getting started. I hate reading docs. I want to scan them quickly. Examples let me do that.

I would contribute but I'd need an expert to translate these things as I couldn't find them in the Javadoc.