Create an init type for AsciiDoc (.adoc)

[jaredmorgs]

I would have a go at creating an init type for .adoc files, but I'm not sure how the CLI hangs together that well.

For this reason, could I please request that you add an .adoc init type to the CLI so we can provision a new book using basic .adoc files and syntax in the files.

This would then allow you to add an .adoc option to the [Online | Mac | Windows] editors when creating a book so users have a clear choice about what

Happy to provide some placeholder content for the files if you think that's appropriate.