Label all intros

communicate.Rmd

@@ -1,6 +1,6 @@
 # (PART) Communicate {-}
 
-# Introduction
+# Introduction {#communicate-intro}
 
 So far, you've learned the tools to get your data into R, tidy it into a form convenient for analysis, and then understand you data through transformation, visualisation and modelling. However, it doesn't matter how great your analysis is unless you can explain it to others: you need to __communicate__ your results.
 

explore.Rmd

@@ -1,6 +1,6 @@
 # (PART) Explore {-}
 
-# Introduction
+# Introduction {#explore-intro}
 
 The goal of the first part of this book is to get you up to speed with the basic tools of data exploration as quickly as possible:
 

program.Rmd

@@ -1,6 +1,6 @@
 # (PART) Program {-}
 
-# Introduction
+# Introduction {#program-intro}
 
 In this part of the book, you'll enrich your programming skills. Programming is a cross-cutting skill needed for all data science work. You must use a computer; you cannot do it in your head, nor with paper and pencil. And to work efficiently, you will need to know how to program in a computer language, such as R.