added readme, moved files

post/merge-scalar-data-arrays/README.md

+# Merge two scalar data arrays
+
+This script takes two scalar nodal fields from a vtu file and combines them to a
+two-component vector field.
+

post/mergeDataArrays.py → post/merge-scalar-data-arrays/mergeDataArrays.py

@@ -11,7 +11,7 @@
 from vtk import *
 from sys import argv, exit
 
-if len(argv) < 6:
+if len(argv) != 6:
     print "Usage:", argv[0], "input.vtu scalar1 scalar2 vector_2d output.vtu"
     exit(1)