I couldn't find a specific place for documentation bugs...
Minor isssue: At http://ngspice.sourceforge.net/ngspice-tutorial.html , I think the text "The voltage at input node 'int' rises so fast that you do not see its slope" should read "The voltage at input node 'in' rises so fast that you do not see its slope"
s/int/in/
Thanks for the report.
A fix is uploaded.