R降级标题索引

Question

我见过能够根据您R降价文档中的标题创建索引的人，如这张图片所示

如果有人能让我知道我该如何修改此代码，以便它创建该左索引表？

---
title: "Untitled"
author: "Juan Lozano"
date: "October 19, 2018"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

## Title 1

Text Text Text Text Text

```{r cars}
summary(cars)
```

## Title 2

Text Text Text Text Text

Answer 1

@hrbrmstr的链接表明可能有许多YAML定制： 这是我通常使用的那种东西：

---
title: "Untitled"
author: "john Smith"
date: "today ;)"
output:
  html_notebook:
    fig_caption: yes
    number_sections: yes
    toc: yes
    toc_float: yes
  html_document:
    fig_caption: yes
    number_sections: yes
    toc: yes
    toc_float: yes
    df_print: paged
bibliography: /path/to/library.bib
---