documentation: clarifications about the Python language

INSTALL

@@ -6,7 +6,7 @@ Prerequisites
 =============
 
 Building kwant requires
- * `Python <http://python.org>`_ 2.6 or newer,
+ * `Python <http://python.org>`_ 2.6 or 2.7 (Python 3 is not supported yet),
  * `SciPy <http://scipy.org>`_ 0.7.2 or newer,
  * `LAPACK <http://netlib.org/lapack/>`_ and `BLAS <http://netlib.org/blas/>`_,
    (For best performance we recommend the free `OpenBLAS

doc/source/tutorial/introduction.rst

 Introduction
 ============
 
+The Python programming language
+...............................
+
+kwant is a library for `Python <http://python.org/>`_.  Care was taken to fit
+well with the spirit of the language and to take advantage of its expressive
+power.  If you do not know Python yet, do not fear: Python is widely regarded
+as one of the most accessible programming languages.  For an introduction we
+recommend the `official Python Tutorial <http://docs.python.org/2/tutorial/>`_.
+The `Beginner's Guide to Python <http://wiki.python.org/moin/BeginnersGuide>`_
+contains a wealth of links to other tutorials, guides and books including some
+for absolute beginners.
+
+kwant
+.....
+
 There are two steps in obtaining a numerical solution to a problem: The first
 is defining the problem in a computer-accessible way, the second solving it.
 The aim of a software package like kwant is to make both steps easier.
@@ -25,10 +40,6 @@ as a lead and attached to a another system.  If both systems have sites which
 belong to the same lattices, the attaching can be done automatically, even if
 the shapes of the systems are irregular.
 
-kwant is a library for the `Python <http://python.org/>`_ programming language.
-Care was taken to fit well with the spirit of the language and to take
-advantage of its expressive power.
-
 Once a tight binding system has been created, solvers provided by kwant can be
 used to compute physical observables.  Solvers expect the system to be in a
 different format than the one used for construction -- the system has to be