Run pod install.

TwitterInstant git:(master) pod install
Analyzing dependencies
Downloading dependencies
Installing ReactiveCocoa (2.1.7)
Generating Pods project
Integrating client project

[!] From now on use `TwitterInstant.xcworkspace`.

[!] CocoaPods was not able to update the `master` repo. If this is an unexpected issue and persists you can inspect it running `pod repo update --verbose`