update doc

content/doc/index.txt

 Kwant documentation
 ===================
 
-The two available resources for learning Kwant are its documentation, and the
-paper introducing Kwant structure and design. The documentation contains
-tutorial and package reference. The tutorial part of the documentation is
-hands-on, and mainly explains how to use Kwant and its various features. The
-package reference provides detailed description of every Kwant
-component. Finally, the paper presents a more general
-perspective, that is useful to kwow for extending Kwant functionality.
+Kwant is accompanied by extensive documentation that contains a hands-on
+tutorial and a complete reference.  In addition, a scientific article exists
+that introduces Kwant in a more structured way and discusses its design and
+performance.
 
-Kwant documentation:
+Kwant documentation (including tutorial):
 
 * `browse online </doc/1.0>`_
-* `download pdf <http://downloads.kwant-project.org/doc/kwant-doc-1.0.0.pdf>`_
-* `download html+zip
-  <http://downloads.kwant-project.org/doc/kwant-doc-1.0.0.zip>`_
+* `download PDF <http://downloads.kwant-project.org/doc/kwant-doc-1.0.0.pdf>`_
+* `download zipped HTML
+  <http://downloads.kwant-project.org/doc/kwant-doc-1.0.0.zip>`_ (for reading
+  without web access)
 
 Kwant paper:
 
-* `download pdf <http://downloads.kwant-project.org/doc/kwant-paper.pdf>`__
+* `download PDF <http://downloads.kwant-project.org/doc/kwant-paper.pdf>`__