more info on output in docs

docs/source/usage/plugins/xrayScattering.rst

@@ -115,8 +115,22 @@ Output
 
 ``<species>_xrayScatteringOutput.<backend-specific extension>``
 
-Output file in the `openPMD` standard. 
+Output file in the `openPMD` standard. An example on how to access your data with the python reader:
 
+.. code-block:: python
+
+    from picongpu.plugins.data import XrayScatteringData
+
+    simulation_path = '...' # dir containing simOutput, input, ..,
+    # Read output from the 0th step, for electrons, hdf5 backend.
+    data = XrayScatteringData( simulation_path, 'e', 'h5' )
+    amplitude = saxsData.get(iteration=0) * saxsData.get_unit()
+    del XrayScatteringData
+
+When you don't want to use the python reader keep in mind that:
+ * All iterations are saved in a single file
+ * The mesh containing the output is called `'amplitude'`
+ * This mesh has 2 components,  `'x'` is the real part and `'y'` is the imaginary part.
 .. note::
     The amplitude is not zeroed on ``outputPeriod`` so one has to subtract the output from the iteration one period before and then calculate :math:`\left|\Phi\right|^2` and sum it with the intensities from other coherence periods.