Update the read me

README.txt

@@ -47,3 +47,19 @@ Getting help and having news from us:
 You can subscribe to the scalfmm users mailing list ( scalfmm-public-users@lists.gforge.inria.fr,  http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/scalfmm-public-users ). Very low trafic (~ 2 mails per year) just to know when a news version or an improvement is available.
 
 Contact the developers at : scalfmm-public-support@lists.gforge.inria.fr
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+
+---------------------------------------------------
+---------------------------------------------------
+
+What inside :
+=============
+× Src : The Core of Scalfmm is under the Src directory. Users should not need to modify the source.
+One can want to implement its own kernel or even its own parallelization whithout modifying the sources.
+× Data : example of particles distributions
+× Examples : examples of very common usage of Scalfmm
+× Doc : should contains the generated Doc
+× UTests : contains some unit tests (it can be a good example to understand some features)
+× Tests : examples to know how to use scalfmm/put particles in the tree/iterate on the tree...
+× Utils : some scripts to work with the data files.
+