introduction: fix link to "Bitcoin Fundamentals Review" appendix (#661)

01_introduction.asciidoc

@@ -10,7 +10,7 @@ Today, in 2021, the Lightning Network is still in its infancy. The Lightning Net
 The concept of the Lightning Network was proposed in 2015, and the first implementation was launched in 2018. As of 2021, we're only beginning to see the opportunities the Lightning Network provides to Bitcoin including improved privacy, speed, and scale.
 With core knowledge of the Lightning Network, you can help shape the future of the network while also building opportunities for yourself.
 
-We assume you already have some basic knowledge about Bitcoin, but if not, don't worry – we will explain the most important Bitcoin concepts, those you must know to understand the Lightning Network, in <<bitcoin_fundamentals>>. If you want to learn more about Bitcoin, you can read _Mastering Bitcoin_, available for free online.
+We assume you already have some basic knowledge about Bitcoin, but if not, don't worry – we will explain the most important Bitcoin concepts, those you must know to understand the Lightning Network, in <<bitcoin_fundamentals_review>>. If you want to learn more about Bitcoin, you can read _Mastering Bitcoin_, available for free online.
 
 While the bulk of this book is written for programmers, the first few chapters are written to be approachable by anyone regardless of technical experience. In this chapter, we'll start with some terminology, then move to looking at trust and its application in these systems, and finally we'll discuss the history and future of the Lightning Network. Let's get started.