improve docstrings in termsBiot.py
improve docstrings in termsBiot.py

sfepy/sfepy,RexFuzzle/sfepy,RexFuzzle/sfepy,vlukes/sfepy,rc/sfepy,lokik/sfepy,vlukes/sfepy,RexFuzzle/sfepy,olivierverdier/sfepy,olivierverdier/sfepy,RexFuzzle/sfepy,rc/sfepy,lokik/sfepy,rc/sfepy,BubuLK/sfepy,BubuLK/sfepy,sfepy/sfepy,sfepy/sfepy,vlukes/sfepy,lokik/sfepy,BubuLK/sfepy,lokik/sfepy,olivierverdier/sfepy