Give introductions section numbers

advanced-ui.Rmd

@@ -10,7 +10,7 @@ library(htmltools)
 library(magrittr)
 ```
 
-## Introduction {-}
+## Introduction
 
 The native languages of the web are HTML (for content), CSS (for styling), and JavaScript (for behavior). Shiny is designed to be accessible for R users who aren't familiar with any of those languages. But if you do speak these languages, you can take full advantage of them with Shiny to customize your apps or extend the Shiny framework.
 

basic-ui.Rmd

@@ -4,7 +4,7 @@
 source("common.R")
 ```
 
-## Introduction {-}
+## Introduction
 
 As you saw in the previous chapter, Shiny encourages separation of the code that generates your user interface (`ui`) from the code that drives your app's behavior (`server`). In this chapter, we'll dive deeper into the UI side of things.
 

reactivity-demystifying.Rmd

@@ -6,7 +6,7 @@
 source("common.R")
 ```
 
-## Introduction {-}
+## Introduction
 
 In this chapter, we'll form a mental model of reactive programming. Without reactive programming, Shiny would not exist, and in well-informed hands it is by far the most elegant, robust, and productive way we know of for creating dynamic user interfaces.
 

reactivity-intro.Rmd

@@ -1,6 +1,6 @@
 # Reactive programming basics
 
-## Introduction {-}
+## Introduction
 
 In the previous chapters, we talked about creating user interfaces. Now we'll move on to discuss the server side of Shiny, where we use R code at runtime to make our user interfaces come alive!
 

your-first-app.Rmd

@@ -1,6 +1,6 @@
 # Your first Shiny app
 
-## Introduction {-}
+## Introduction
 
 In this chapter, we'll create a simple Shiny app. Along the way, you'll learn the basic structure of a Shiny app, and how to save and run Shiny apps using the RStudio IDE. You'll also take your first steps into reactive programming.