docs: fix table of contents in users guide
docs: fix table of contents in users guide

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