Support README.adoc or CONTRIBUTORS.adoc (asciidoc / asciidoctor)

**Is your feature request related to a problem? Please describe.**

Not related to a problem.

**Describe the solution you'd like**

```json
{
"documentType" : "adoc"
}
```

Global, or just figure it out by file extension (`files`).

**Describe alternatives you've considered**

Including `CONTRIBUTORS.md` in my `README.adoc`, but that does not work.

**Additional context**

AsciiDoc is probably simpler to code.