renderAuditGroup(group) {
    const groupEl = this.dom.createElement('div', 'lh-audit-group');

    const auditGroupHeader = this.dom.createElement('div', 'lh-audit-group__header');

    this.dom.createChildOf(auditGroupHeader, 'span', 'lh-audit-group__title')
      .textContent = group.title;
    groupEl.append(auditGroupHeader);

    let footerEl = null;
    if (group.description) {
      footerEl = this.dom.convertMarkdownLinkSnippets(group.description);
      footerEl.classList.add('lh-audit-group__description', 'lh-audit-group__footer');
      groupEl.append(footerEl);
    }

    return [groupEl, footerEl];
  }
Renders the group container for a group of audits. Individual audit elements can be added
directly to the returned element.
@param {LH.Result.ReportGroup} group
@return {[Element, Element | null]}