small fixes in doc/users_guide.rst
small fixes in doc/users_guide.rst

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