Link to the building doc fixed.

README.txt

@@ -1,4 +1,3 @@
-
 Thank you for downloading logback, the reliable, generic, fast and
 flexible logging library for Java.
 
@@ -9,7 +8,7 @@ Building logback
 
 Building logback is documented at:
 
-  http://logback.qos.ch/manual/introduction.html#BuildingLogback
+  http://logback.qos.ch/setup.html#ide
 
 In case of problems
 ===================
@@ -19,4 +18,4 @@ on the logback-user@qos.ch mailing list.  However, please do not
 directly e-mail logback developers. The answer to your question might
 be useful to other users. Moreover, there are many knowledgeable users
 on the logback-user mailing lists who can quickly answer your
-questions. 
+questions.