Update doc/en/writing_plugins.rst
Update doc/en/writing_plugins.rst

Co-authored-by: Ran Benita <24765b4c90fc2e23473c676ae4ed89a28c4ecf1e@unusedvar.com>
markshao/pytest,Akasurde/pytest,nicoddemus/pytest,pytest-dev/pytest,nicoddemus/pytest,RonnyPfannschmidt/pytest