Added Carthage in installation instructions

Author: dinhvh

build-mac/README.md

@@ -1,3 +1,9 @@
+### Carthage ###
+
+MailCore 2 is available through [Carthage](https://github.com/Carthage/Carthage).
+
+[![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)
+
 ### Cocoapods ###
 
 MailCore 2 is available on [Cocoapods](http://cocoapods.org/).