Show how to configure auto-completion in IntelliJ

Could you please extend the examples to also make auto-completion, e.g. in `hello-kotlinx-html.scriptwithdeps.kts`, work in IntelliJ?

For example, if I'm extending `ScriptWithMavenDeps` with a dummy property like

```
abstract class ScriptWithMavenDeps {
val dummy: String = "oink"
}
```

what does it take to offer `dummy` when typing `this.` in `hello-kotlinx-html.scriptwithdeps.kts`?

Start with hello-kotlinx-html.scriptwithdeps.kts and the ScriptWithMavenDeps example in the issue, then investigate how IntelliJ is configured for this script. Done means the example explains or demonstrates a setup where typing this. offers the dummy property for completion.

Written by the indexing model from the issue text.