Update Readme

Add Swift Package manager reference

Author: alessioarsuffi

README.md

@@ -0,0 +1,21 @@
+# Marvin
+
+## Installation
+
+### Swift Package Manager
+```
+dependencies: [
+    .package(url: "https://github.com/monksoftware/Marvin.git", from: "1.0.0")
+]
+```
+
+### Carthage
+```
+github 'monksoftware/Marvin'
+```
+
+Made with ❤️ in Italy, by [Monk](https://www.monksoftware.it "Monk's homepage")
+
+<p align="left" >
+<img src="https://github.com/monksoftware/Marvin/blob/master/monk-logo.png" width=200px height=50px alt="Marvin" title="Marvin">
+</p>