please tell me default templates

## Background
I have created some terraform provider,
and it is need to create document so using this and modify but I have a hard time reproducing default.

I have copy and paste from [template.go](https://github.com/hashicorp/terraform-plugin-docs/blob/main/internal/provider/template.go) but something wrong...for example, not output Example Usage on index.md.
(What is `{{ if .HasExample -}}` ...?)

## I need...
- how to reproduce default
- default templates on `(this repo)/templates/*`
- documentation special variables/functions

Thank you.