27.8 Multiple authors in R Markdown

From https://community.rstudio.com/t/rmarkdown-cant-keep-authors-in-separate-lines/65183:

---
title: "R Markdown v2 Demo"
author:
  - John
  - Joe
date: "2015/01/01"
output: pdf_document
header-includes: 
  - \renewcommand{\and}{\\}
---

Hello world.