Changed the module description.

When run from the terminal, the code runs in two modes.

 First mode:

  'python CSLgenerator.py u v w [limit]' ----->  Where the u v w are the

  'csl_generator.py u v w [limit]' ----->  Where the u v w are the

  indices of the rotation axis such as 1 0 0, 1 1 1, 1 1 0 and so on. The limit

  is the maximum Sigma of interest.

  (the limit by default: 100)

 Second mode:

 'python CSLgenerator.py u v w basis sigma [limit]' -----> Where basis is

 'csl_generator.py u v w basis sigma [limit]' -----> Where basis is

  either fcc, bcc, diamond or sc. You read the sigma of interest from the first

  mode run. The limit here refers to CSL GB inclinations. The bigger the limit,

  the higher the indices of CSL planes.

 values. For ex.: input the GB_plane of interest from  running the CSl_generator

 in the second mode. Once you have completed customizing the io_file, run:

 'python gb_generator.py io_file'

 'gb_generator.py io_file'

 """

import sys