correct punctuation

Author: adavidw

README.md

@@ -17,7 +17,7 @@ You can also run each sample directly from the command line.
 ```
     $ git clone https://github.com/AuthorizeNet/sample-code-csharp.git
 ```
-* Include the [Authorize.Net .NET SDK](https://github.com/AuthorizeNet/sdk-dotnet)
+* Include the [Authorize.Net .NET SDK](https://github.com/AuthorizeNet/sdk-dotnet):
  `PM> Install-Package AuthorizeNet`  
  Build the project to produce the SampleCode console app.
 * Run the individual samples by name. For example: