Extend intro, and move bug note

This elaborates the intro a little, and moves the bug note (since I do
not consider it to be so important to be at the very beginning).

Author: ehuss

src/introduction.md

@@ -1,9 +1,6 @@
 # Introduction
 
-This book is the primary reference for the Rust programming language.
-
-> [!NOTE]
-> For known bugs and omissions in this book, see our [GitHub issues]. If you see a case where the compiler behavior and the text here do not agree, file an issue so we can think about which is correct.
+This book is the primary reference for the Rust programming language. It serves as a description of the syntax, semantics, and interpretation of the Rust language.
 
 ## Rust releases
 
@@ -35,6 +32,9 @@ The second is to generally improve your knowledge of a facet of the language. In
 
 That said, there is no wrong way to read this book. Read it however you feel helps you best.
 
+> [!NOTE]
+> For known bugs and omissions in this book, see our [GitHub issues]. If you see a case where the compiler behavior and the text here do not agree, file an issue so we can think about which is correct.
+
 ### Conventions
 
 Like all technical books, this book has certain conventions in how it displays information. These conventions are documented here.