en: contribute: Update the description of support version of Python
en: contribute: Update the description of support version of Python

Signed-off-by: Shinpei Muraoka <154d36ff5308ea67e46435bebcfb51dcc823bd4d@gmail.com>

iwaseyusuke/ryu-book,osrg/ryu-book,osrg/ryu-book,iwaseyusuke/ryu-book