chapter01, index: Fix translation of "introduction"

chapter01/chapter01.xml

@@ -9,7 +9,7 @@
   <?dbhtml dir="chapter01"?>
   <?dbhtml filename="chapter01.html"?>
 
-  <title>介绍</title>
+  <title>引言</title>
 
   <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="how.xml"/>
   <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="whatsnew.xml"/>

index.xml

@@ -12,7 +12,7 @@
 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="prologue/preface.xml"/>
 
 <part id="part1">
-<title>介绍</title>
+<title>引言</title>
 <?dbhtml filename="part1.html"?>
 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="chapter01/chapter01.xml"/>
 </part>