docs: update users guide for pytest-related changes
docs: update users guide for pytest-related changes

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