add usage.md

Author: rohitdaryanani

README.md

@@ -15,7 +15,7 @@ If you are looking for the SendGrid API client library, please see [this repo](h
 * [Announcements](#announcements)
 * [Installation](#installation)
 * [Quick Start](#quick-start)
-* [Usage](#usage)
+* [Library Usage Documentation](USAGE.md)
 * [Roadmap](#roadmap)
 * [How to Contribute](#contribute)
 * [Thanks](#thanks)
@@ -89,8 +89,6 @@ Console.WriteLine(response.Headers.ToString());
 <a name="usage"></a>
 # Usage
 
-- [Example Code](https://github.com/sendgrid/csharp-http-client/blob/master/Example/Example.cs)
-
 <a name="roadmap"></a>
 # Roadmap
 

USAGE.md

@@ -0,0 +1 @@
+- [Example Code](https://github.com/sendgrid/csharp-http-client/blob/master/Example/Example.cs)