[doc] add some general information

doc/index.rst

 tomoscan
 ========
 
+tomoscan aims to provide an unified interface to read tomography data from .edf or .hdf5 (NXtomo) acquisitions.
+
 .. toctree::
    :maxdepth: 4
 

tomoscan/esrf/edfscan.py

@@ -22,6 +22,8 @@
 #
 #############################################################################*/
 
+"""contains EDFTomoScan, class to be used with EDF acquisition"""
+
 
 __authors__ = ["H.Payno"]
 __license__ = "MIT"

tomoscan/esrf/hdf5scan.py

@@ -22,6 +22,8 @@
 #
 #############################################################################*/
 
+"""contains EDFTomoScan, class to be used with HDF5 acquisition"""
+
 
 __authors__ = ["H.Payno"]
 __license__ = "MIT"