async function register(grammars) {
    currentRegistry = await createRegistry(grammars)
  }
Add more grammars.

@param {ReadonlyArray<Readonly<Grammar>>} grammars
  Grammars to support.
@returns {Promise<undefined>}
  Promise resolving to nothing.
@example
  ````js
  import {createStarryNight} from '@wooorm/starry-night'
  import sourceCss from '@wooorm/starry-night/source.css'
  import textMd from '@wooorm/starry-night/text.md'
  import {toHtml} from 'hast-util-to-html'

  const markdown = '```css\nem { color: red }\n```'

  const starryNight = await createStarryNight([textMd])

  console.log(toHtml(starryNight.highlight(markdown, 'text.md')))

  await starryNight.register([sourceCss])

  console.log(toHtml(starryNight.highlight(markdown, 'text.md')))
  ````

  Yields:

  ````html
  <span class="pl-s">```</span><span class="pl-en">css</span>
  <span class="pl-c1">em { color: red }</span>
  <span class="pl-s">```</span>
  ````

  ````html
  <span class="pl-s">```</span><span class="pl-en">css</span>
  <span class="pl-ent">em</span> { <span class="pl-c1">color</span>: <span class="pl-c1">red</span> }
  <span class="pl-s">```</span>
  ````