You can now add as many Rmarkdown files as you want for your content. Each one will be processed into an html file. For example in Test Website, we have two files, about.Rmd and contact.Rmd. Your Rmd files should have the yaml at top and then your Rmarkdown content.

Here is a simple example.

---
title: Simple Rmd File
---

Here is a simple file.

about.Rmd is a fuller Rmd file with R code and figures.

If you want the file linked to in your top nav bar, then add it to _site.yml.

name: "my-website"
output_dir: "."
navbar:
  title: "My Website"
  left:
    - text: "About"
      href: about.html
    - text: "Contact"
      icon: fa-user-circle
      href: contact.html
output:
  html_document:
    theme: readable
    toc_depth: 3
    toc_float:
      collapsed: false