add more info to README for 1.2.6
add more info to README for 1.2.6

CarlosCD/airbrake,CarlosCD/airbrake,airbrake/airbrake,thoughtbot/hoptoad_notifier,benjaminoakes/airbrake,nick-desteffen/airbrake,Shopify/airbrake,kakra/hoptoad_notifier,nick-desteffen/airbrake,thoughtbot/airbrake,stevecrozz/hydraulic_brake,airbrake/airbrake,square/hoptoad_notifier