Added Customizing the Bot section to describe plugins pattern.
Added Customizing the Bot section to describe plugins pattern.

vadim-skorba/starter-python-bot,Fluberto/flysprayslackbot,Zefiros-Software/Zefiros-Bot,torgeirl/eliza,alexanderlukanin13/slack-bot,BeepBoopHQ/starter-python-bot,torgeirl/tradingpost-beepboop,Mechdriver/slack-christmas-bot,Anthony-Handwerker/mtg-buddy-2,ramseymcgrath/MFWBot,dronesoc/dronebot,torgeirl/tradingpost,gh0stcaesar/vocaloid_bot2,gigadeleo/starter-python-bot,eedeebee/usher-bot,ermontross/ProjectBot,SpyDeX/BeepMiBot,gbritt/grossmanbot,evilcandybag/cardfetcher_prime,coderSharma/starter-python-bot,Mechdriver/slack-christmas-bot,joshmgross/slack-quote-bot,shamitb/Tantal,oradwastaken/slack-python-latexbot,EndermanAPM/silbot_slack,zhongzho/starter-python-bot,anseljh/casebot-beepboop,eedeebee/usher-bot,midiprincess/slackday-code-review-bot,ArthurMoore85/rb5-slack-bot,valeraz/crbot,zhongzho/starter-python-bot,god-hirosi/resas,tangc88/leaguebot