DOC: Improve README file

Some newcommers will read the readme file first,
for example visitors from Github.  Add an introduction
paragraph and links to important web ressources.

README

-This is the ORFEO Toolbox README file.
-Please see the Copyright directory for legal issues on the use of the software.
-Install information is available in the OTB Software Guide which can be downloaded from http://www.orfeo-toolbox.org.
-
-Please report any issue you might encouter to our bugtracker; http://bugs.orfeo-toolbox.org
-
-Thank you.
-
-The OTB Development Team.
-
-

README.md

+# Orfeo Toolbox
+## Open Source processing of remote sensing images
+![OTB](https://git.orfeo-toolbox.org/otb.git/blob_plain/HEAD:/Utilities/Doxygen/logoVectoriel.png)
+
+Orfeo ToolBox (OTB) is an open-source C++ library for remote sensing images
+processing, distributed under the CeCILL-v2 license.  It has been initiated and
+funded by CNES (French space agency) in the frame of a program named ORFEO to
+prepare, accompany and promote the use and the exploitation of the images
+derived from Pléiades satellites (PHR). Orfeo ToolBox aims at enabling large
+images state-of-the-art processing even on limited resources laptops, and is
+shipped with a set of extensible ready-to-use tools for classical remote sensing
+tasks, as well as a fully integrated, end-users oriented software called
+Monteverdi.
+
+### Ressources
+* [OTB's website](https://www.orfeo-toolbox.org/)
+* [Documentation](https://www.orfeo-toolbox.org/documentation/)
+* [Downloads](https://www.orfeo-toolbox.org/download/)
+* [Public git repositories](https://git.orfeo-toolbox.org/)
+* [GitHub mirror](https://github.com/orfeotoolbox/)
+* [Build status](http://dash.orfeo-toolbox.org/index.php?project=OTB)
+* [Bug tracker](https://bugs.orfeo-toolbox.org/)
+* [Wiki](http://wiki.orfeo-toolbox.org/index.php/Main_Page)
+* [Task tracking](http://scrum.orfeo-toolbox.org)
+
+### Join the community
+Get help, share your experience and contribute to the Orfeo-Toolbox project by
+joining our community and mailing lists.
+
+[https://www.orfeo-toolbox.org/community/](https://www.orfeo-toolbox.org/community/)
+
+### Contributing
+Please see the wiki for contributors guidelines.
+
+### License
+Please see the license and the Copyright directory for legal issues on the use of the software.
+
+### Issues
+Please report any issue you might encouter to [our bugtracker](http://bugs.orfeo-toolbox.org).
+