Doc: added panorama image + intro text

Author: PierreRaybaut

doc/images/panorama.png

@@ -32,6 +32,7 @@ entire curve is still painted (in other words, when working with large
 amount of data, there is no performance gain when zooming in).
 
 Other API compatibility issues with `Qwt`:
-- `QwtPlot.MinimizeMemory` option was removed as this option has no sense 
-  in python-qwt (the polyline plotting is not taking more memory than the 
-  array data that is already there).
+
+    - `QwtPlot.MinimizeMemory` option was removed as this option has no sense 
+      in python-qwt (the polyline plotting is not taking more memory than the 
+      array data that is already there).

doc/overview.rst

@@ -4,7 +4,23 @@
 # Copyright (c) 2002 Uwe Rathmann, for the original C++ code
 # Copyright (c) 2015 Pierre Raybaut, for the Python translation/optimization
 # (see LICENSE file for more details)
+"""
+python-qwt
+==========
 
+The ``python-qwt`` package is a 2D-data plotting library using Qt graphical 
+user interfaces for the Python programming language.
+
+It consists of a single Python package named `qwt` which is a pure Python 
+implementation of Qwt C++ library with some limitations.
+
+.. image:: images/panorama.png
+
+External resources:
+    * Bug reports and feature requests: `GitHub`_
+
+.. _GitHub: https://github.com/PierreRaybaut/python-qwt
+"""
 __version__ = '0.1.1'
 QWT_VERSION_STR = '6.1.2'