Fabric now supports installation with CocoaPods: http://docs.fabric.io/ios/fabric/cocoapods.html
If you are just looking for Crashlytics you can use these two pods:
pod 'Fabric'
pod 'Crashlytics'
Along with adding the following build phase script (note: In case the path to your repo contains spaces, you will need the quotes):
"${PODS_ROOT}"/Fabric/run <API Key> <Build Secret>
If you are looking to use TwitterKit you will need to include:
pod 'TwitterKit'