[eslint] add readme to eslint-config-airbnb
[eslint] add readme to eslint-config-airbnb

pokelondon/javascript,airbnb/javascript,ljharb/javascript,naustudio/javascript,LodoSoftware/javascript-style-guide,webcoding/javascript-style-guide,allanfish/javascript,getjll/JavaScript-Style-Guide,codelegant/JavaScript,whichdigital/javascript-coding-standards,codelegant/JavaScript,naustudio/javascript,addshoppers/javascript,LodoSoftware/javascript-style-guide,nulogy/javascript,bl00mber/javascript,appcom-interactive/javascript,practicefusion/javascript,cloudability/javascript-style-guide,xalexec/javascript