some details based on #1221

I just copied Objective-C.gitignore. It seemed to do the job with a small Swift
project.

This got changed recently.

xcuserstate files are generated from within Xcode and saved in your project bundle to remember your last opened file, the open state of any group folders, open tabs, and any other user setting your project might need to remember

We shouldn't be ignoring these, it's down to the user and we shouldn't enforce them to ignore the `Pods/` directory

http://guides.cocoapods.org/using/using-cocoapods.html#should-i-ignore-the-pods-directory-in-source-control?

The pattern `*.xccheckout` is already ignored on line 15.

This is a file that Xcode 5 uses for version control, doesn't need to be checked in. Also see http://stackoverflow.com/a/18448100/1877078

Per discussion in #148.

Reverted a change that was causing build directories at the root folder to show up in git.  If you need to ignore subdirectories the leading slash needs to be omitted.

Workspaces are real documents that can be opened, just like `xcodeproj`
documents. These documents are also generated/used by CocoaPods to
configure a project’s dependencies. For these reasons, there does not
seem a good reason to ignore these any longer.

DerivedData is the "build/" Folder that *might* be in your Project's folder if you use the default Xcode 4 settings.