Explain in README how to use custom templates

[mojavelinux]

Explain how to use custom templates for generating HTML output from AsciiDoc. Here are the requirements:

• Add additional gems (the gem for the template engine as well as the thread_safe gem)
• Create the _templates directory in the project root
• Add at least one template to the _templates directory
• Enable the template_dir option in the Asciidoctor configuration in _config.yml

[mojavelinux]

Here are the steps.

Step 1: Add additional gems to the Gemfile

gem 'slim', '~> 3.0.7'
gem 'thread_safe', '~> 0.3.5'

Step 2: Run Bundler

$ bundle

Step 3: Create a folder for templates named _templates

$ mkdir _templates

Step 4: Add a template to the _templates folder (ulist.html.slim)

- if title?
  figure.list.unordered id=id
    figcaption=title
    ul class=[style, role]
      - items.each do |_item|
        li
          span.primary=_item.text
          - if _item.blocks?
            =_item.content
- else
  ul id=id class=[style, role]
    - items.each do |_item|
      li
        span.primary=_item.text
        - if _item.blocks?
          =_item.content

Step 5: Configure Asciidoctor in _config.yml to use templates

asciidoctor:
  template_dir: _templates
  attributes:
    ...