Fix example mistake

examples/SedovBlast_3D/sedov.yml

@@ -19,7 +19,8 @@ Snapshots:
   time_first:          0.    # Time of the first output (in internal units)
   delta_time:          1e-2  # Time difference between consecutive outputs (in internal units)
   compression:         4
-  
+  FieldsFilename:      ../output_fields_example.yml 
+ 
 # Parameters governing the conserved quantities statistics
 Statistics:
   delta_time:          1e-3 # Time between statistics output