Update README.md

Author: cargath

README.md

@@ -1,3 +1,26 @@
 # MarvelKit
 
 A Swift SDK for working with the https://developer.marvel.com/ API.
+
+## Usage
+
+    let client = MarvelKit(privateKey: "abcd", publicKey: "1234")
+    
+    func performRequest() {
+        client
+            .request(Comic.self)
+            .withParameters([.DateRange(NSDate(timeIntervalSinceReferenceDate: 0), NSDate()), .Limit(2)])
+            .exec(success: onSuccess, error: onError)
+    }
+
+    func onSuccess(comicDataWrapper: ComicDataWrapper) {
+        print(comicDataWrapper)
+    }
+
+    func onError(error: MarvelKitError) {
+        print(error.description)
+    }
+
+## Acknowledgements
+
+I'm using the MD5 related bits from https://github.com/krzyzanowskim/CryptoSwift by Marcin Krzyżanowski until CommonCrypto works better with Swift. I could have used a Wrapper framework, but i didn't want to introduce a dependency and thought this was a great opportunity to see how MD5 is implemented.