new define() in sinbc.py example, update docstring
new define() in sinbc.py example, update docstring

vlukes/sfepy,sfepy/sfepy,rc/sfepy,vlukes/sfepy,vlukes/sfepy,sfepy/sfepy,rc/sfepy,BubuLK/sfepy,sfepy/sfepy,BubuLK/sfepy,rc/sfepy,BubuLK/sfepy