added explanation where to find detailed instructions how to compile (proposed by Marc Dorchain)

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@193422 13f79535-47bb-0310-9956-ffa450edef68

README

@@ -14,5 +14,7 @@ FOP readme
     HTML-Documentation can be found in the subdirectory /docs. 
 
     Compilation of Fop is started by executing build. It requires
-    Xerces-J, Xalan and bsf.jar (comes with Xalan) in your classpath.
+    Xerces-J, Xalan and bsf.jar (comes with Xalan) in your classpath. 
+    You can find more details in build.xml or in the documentation under the 
+    heading 'compiling'.