Update archivebot.py documentation
Update archivebot.py documentation

Noting that %(monthname)s does support local language and not only
English as stated before.

Bug: T169719
Change-Id: I7a0dd192c7b632c36a673cb7050d095d0dc8ca54

hasteur/g13bot_tools_new,magul/pywikibot-core,hasteur/g13bot_tools_new,PersianWikipedia/pywikibot-core,wikimedia/pywikibot-core,wikimedia/pywikibot-core,npdoty/pywikibot,happy5214/pywikibot-core,magul/pywikibot-core,hasteur/g13bot_tools_new,npdoty/pywikibot,happy5214/pywikibot-core