[Doc] Add IO info

[ci-skip]

doc/introduction/data-io.rst

@@ -49,13 +49,19 @@ Output Files
 * VTK Files (``.vtu``): The output data in unstructured grid format.
   It contains multiple datasets:
 
+.. object:: Richards
+  
   - ``head``: Matric head
   - ``K0``: Saturated conductivity
   - ``flux``: Water flux (not reconstructed!)
+  - ``flux_RT<k-1>``: Water flux reconstructed (if enabled!)
   - ``theta_w``: Volumetric water content
   - ``Theta``: Water saturation
+
+.. object:: Transport
   - ``solute``: Solute concentration
   - ``solute_total``: Total solute
+  - ``flux_RT<k-1>``: Solute flux reconstructed (if enabled!)
 
 * VTK Parallel Collection Files (``.pvtu``): Merging multiple VTK files in case
   DORiE is run in parallel.