R Markdown html_notebook : How to set UTF-8 encoding directly in the script?

I have a html_notebook in R Markdown that I saved in UTF-8 in RStudio by doing file > Save with Encoding > UTF-8. When other users open the R Markdown file on their computer, the UTF-8 encoding is lost and replaced with their local encoding (Général becomes Général, for example).

Is there a way to "force" an encoding for the other users on a html_notebook, without manual intervention from them? In other words, I wan them to simply open and run the script without having to change their default local encoding.

Is there a way to set the encoding of a R Markdown html_notebook directly in the YAML header settings like the one below, for example? Adding encoding: UTF-8 doesn't seem to be an option.

---
title: "Title"
author: "Author"
date: "September, 2017"
output:
  html_notebook:
    code_folding: none
    df_print: paged
    fig_height: 4
    fig_width: 9
    includes:
      after_body: tabset-dropdown.html
    theme: spacelab
---