[NTG-context] Section numbering starting from zero, not one

[Alex Leray]

Hello,

I'd like to have roman numerals prefixed sections, but starting from 
Zero and not One (even if I know that roman numerals don't have a sign 
for 0).

Is there a way to achieve this? My code looks like that at the moment:

###

\setuphead[section][conversion=Romannumerals]

\starttext
\setupheadnumber[section] [-1]
\startsection[title={Section zero}]\stopsection
\startsection[title={Section one}]\stopsection
\stoptext

###

Thank you,

Alex