Add features to readme (#95)

README.md

@@ -2,6 +2,14 @@
 
 This .NET library provides a structured model of the Dockerfile syntax for the purposes of parsing and generating Dockerfiles. It provides full fidelity of the file contents meaning that the parsed content can be output back to a string and produce the same content character-for-character, including whitespace. This makes it ideal for parsing as well as workflows that require programmatically modifying existing Dockerfiles.
 
+## Key Features
+
+* A high-level model for interacting with Dockerfile constructs.
+* Access to the underlying tokens that make up the higher-level model.
+* Full fidelity for input and output: the model's output is identical to the Dockerfile input.
+* Resolve ARG values that are referenced throughout a Dockerfile.
+* Ability to further organize a Dockerfile model in terms of its stages.
+
 ## Usage
 
 The library is available as a NuGet package: [Valleysoft.DockerfileModel](https://www.nuget.org/packages/Valleysoft.DockerfileModel/).