improve cp_model.py doc
improve cp_model.py doc

google/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools,google/or-tools