Fix some heading issues

base-R.qmd

@@ -8,6 +8,8 @@ source("_common.R")
 status("complete")
 ```
 
+## Introduction
+
 To finish off the programming section, we're going to give you a quick tour of the most important base R functions that we don't otherwise discuss in the book.
 These tools are particularly useful as you do more programming and will help you read code you'll encounter in the wild.
 
@@ -25,6 +27,8 @@ To finish off, we'll briefly discuss two essential plotting functions.
 
 ### Prerequisites
 
+This package focuses on base R so doesn't have any real prerequisites, but we'll load the tidyverse in order to explain some of the differences.
+
 ```{r}
 #| label: setup
 #| message: false

visualize.qmd

@@ -31,11 +31,9 @@ Each chapter addresses one to a few aspects of creating a data visualization.
 
 -   Finally, in @sec-communication you will learn how to take your exploratory graphics and turn them into expository graphics, graphics that help the newcomer to your analysis understand what's going on as quickly and easily as possible.
 
-### Learning more
-
-The absolute best place to learn more is the ggplot2 book: [*ggplot2: Elegant graphics for data analysis (3e)*](https://ggplot2-book.org/).
+These three chapters get you started in the world of visualization, but there is much more to learn.
+The absolute best place to learn more is the ggplot2 book: [*ggplot2: Elegant graphics for data analysis*](https://ggplot2-book.org/).
 It goes into much more depth about the underlying theory, and has many more examples of how to combine the individual pieces to solve practical problems.
-
 Another great resource is the ggplot2 extensions gallery <https://exts.ggplot2.tidyverse.org/gallery/>.
 This site lists many of the packages that extend ggplot2 with new geoms and scales.
 It's a great place to start if you're trying to do something that seems hard with ggplot2.

webscraping.qmd

@@ -7,6 +7,8 @@ source("_common.R")
 status("complete")
 ```
 
+## Introduction
+
 This vignette introduces you to the basics of web scraping with [rvest](https://rvest.tidyverse.org).
 Web scraping is a very useful tool for extracting data from web pages.
 Some websites will offer an API, a set of structured HTTP requests that return data as JSON, which you handle using the techniques from @sec-rectangling.