some updates on classic README, reduce the impression that there is much to install manually;

--- a/README	Fri Apr 27 15:24:37 2012 +0200
+++ b/README	Fri Apr 27 15:59:50 2012 +0200
@@ -7,29 +7,19 @@
    See the NEWS file in the distribution for details on user-relevant
    changes.
 
-System requirements
-
-   Isabelle requires a regular Unix-style platform (e.g. Linux,
-   Windows with Cygwin, Mac OS X) and depends on the following main
-   add-on tools:
+Installation
 
-     * The Poly/ML compiler and runtime system (version 5.2.1 or later).
-     * The GNU bash shell (version 3.x or 2.x).
-     * Perl (version 5.x).
-     * Java 1.6.x from Oracle or Apple -- for Scala and jEdit.
-     * GNU Emacs (version 23 or 24) -- for the Proof General 4.x interface.
-     * A complete LaTeX installation -- for document preparation.
-
-Installation
+   Isabelle work on the three main platform families: Linux, Mac OS X,
+   and Windows (via Cygwin).
 
    Completely integrated bundles including the full Isabelle sources,
    documentation, add-on tools and precompiled logic images for
    several platforms are available from the Isabelle web page.
 
-   Further background information may be found in the Isabelle System
+   Some background information may be found in the Isabelle System
    Manual, distributed with the sources (directory doc).
 
-User interface
+User interfaces
 
    Isabelle/jEdit is an emerging Prover IDE based on advanced
    technology of Isabelle/Scala.  It provides a metaphor of continuous