doc: add basic documentation for install and usage

README.md

@@ -1,4 +1,49 @@
 # Nanoseconds
 
+ ![GitHub Workflow Status](https://img.shields.io/github/workflow/status/dominicegginton/Nanoseconds/CI?label=CI) ![GitHub tag (latest SemVer pre-release)](https://img.shields.io/github/v/tag/dominicegginton/Nanoseconds?include_prereleases&label=release)
+
 > 🕐 Simple high resolution timing for Swift
 
+Nanoseconds is a wrapper around `DispatchTime.now()` providing you with timestamp with nanosecond accuracy.
+
+## Key Features
+
+- High resolution time stamp
+- Built-in operators overloads
+- Useful extensions for unit conversion
+- Linux compatible
+
+## Install
+
+Install via the [**Swift Package Manger**](https://swift.org/package-manager/) by declaring **Spinner** as a dependency in your  `Package.swift`:
+
+``` swift
+.package(url: "https://github.com/dominicegginton/Nanoseconds", from: "0.0.1")
+```
+
+Remember to add **Spinner** to your target as a dependency.
+
+## Usage
+
+Creating high resolution timestamps with nanosecond accuracy is easy:
+
+```  swift
+let foo = Nanoseconds()
+```
+
+Use built-in operators overloads to calculate a [**TimeInterval**](https://developer.apple.com/documentation/foundation/timeinterval):
+
+``` swift
+let start = Nanoseconds()
+sleep(1)
+let end = Nanoseconds()
+let duration = end - start
+print(duration)  //=> 1004222113.0
+```
+
+To convert high resolutions [**TimeInterval**](https://developer.apple.com/documentation/foundation/timeinterval) objects from nanosecond accuracy use a provided extention:
+
+``` swift
+print(duration.milliseconds)  //=> 1004.22211
+print(duration.seconds)  //=> 1.004222113
+```