Reference SPM support

README.md

@@ -5,14 +5,24 @@ native unsigned integer types support.
 
 [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)
 
+## Installation
+This library includes Carthage and SPM support out of the box. Reference this git
+repository in a Cartfile or Package.swift file in order to easily include this library
+while also being able to easily track changes.
+
+You can also manually copy over the Sources/UInt128.swift file into your project and
+it should work great. I've purposely kept this library constrained to a single file in
+order to support this use case.
+
 ## Usage
 Since this library fully implements the UnsignedInteger protocol, you can use this data
 type just like any other native UInt data type. For numbers larger than UIntMax, you'll
 either want to call the `init(upperBits: UInt64, lowerBits: UInt64)` initializer, or,
 use the `init(stringLiteral: String)` initializer to create an instance with a string.
 The string can be in binary, octal, decimal or hexadecimal.
 
-## Example
+For example:
+
     let uInt128ByString: UInt128 = "0xffaabbcc00129823fa9a12d4aa87f498"
     let uInt128ByInteger: UInt128 = 1234