Add PromiseKit dependency

- Added PromiseKit dependency

Carthage/Checkouts/PromiseKit/Extensions/HomeKit/README.markdown

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+# PromiseKit HomeKit Extensions ![Build Status]
+
+This project adds promises to Apple’s HomeKit framework.
+
+* Xcode >= 9.3 required for iOS
+* Xcode >= 9.0 required for all other platforms
+
+Thus, Swift versions supported are: 3.2, 3.3, 3.4, 4.0, 4.1 & 4.2.
+
+## CocoaPods
+
+```ruby
+pod "PromiseKit/HomeKit", "~> 6.0"
+```
+
+The extensions are built into PromiseKit.framework thus nothing else is needed.
+
+## Carthage
+
+```ruby
+github "PromiseKit/HomeKit" ~> 1.0
+```
+
+The extension is built into it's own framework:
+
+```swift
+import PromiseKit
+import PMKHomeKit
+```
+
+
+[Build Status]: https://travis-ci.org/chrischares/PromiseKit-HomeKit.svg?branch=master