Doc update: clarify -W syntax (#9464)
Doc update: clarify -W syntax (#9464)

Co-authored-by: Hugo van Kemenade <5a499df1e6a266942706a9de3d4c03795108f8e3@users.noreply.github.com>
Co-authored-by: Bruno Oliveira <024fc659bb4ab842ec49c8a162b11a29104488bd@gmail.com>
RonnyPfannschmidt/pytest,pytest-dev/pytest,Akasurde/pytest,markshao/pytest