Add "cartspec", updated README.md

Author: greenrobot

README.md

@@ -1,5 +1,5 @@
-# objectbox-swift-spec-staging
+# ObjectBox Staging repository
 
-CocoaPods spec repo for pre-release tests.
+CocoaPods/Carthage spec repo for **pre-release** versions of [ObjectBox Swift](https://github.com/objectbox/objectbox-swift).
 
-**Please get your final versions from the official CocoaPods repository.**
+**THIS IS NOT THE OFFICIAL RELEASE CHANNEL.**

cartspec/ObjectBox.json

@@ -0,0 +1,3 @@
+{
+  "1.1.1": "https://github.com/objectbox/objectbox-swift/releases/download/v1.1.1/ObjectBox-1.1.1-Carthage.framework.zip"
+}

cartspec/README.md

@@ -0,0 +1,14 @@
+ObjectBox Carthage Binary Project Specification
+===============================================
+This folder contains [ObjectBox.json](ObjectBox.json), a [Chartage "index" for binary frameworks](https://github.com/Carthage/Carthage/blob/master/Documentation/Artifacts.md#binary-project-specification).
+The advantage of using binary distribution is that those are slimmer than the "github" definition.
+Using "binary" instead, never causes Carthage to check out the Git repository.
+Thus updates are faster and less disk space is used.
+
+Add binary ObjectBox dependency
+-------------------------------
+In your Cartfile, you typically add a line like this:
+
+    binary "https://raw.githubusercontent.com/objectbox/objectbox-swift/master/cartspec/ObjectBox.json"
+
+For details and up-to-date information, please consult the [installation docs](https://swift.objectbox.io/install).