Add OCI Runtime Abstract

Closes #506

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

spec.md

@@ -2,6 +2,15 @@
 
 The [Open Container Initiative](http://www.opencontainers.org/) develops specifications for standards on Operating System process and application containers.
 
+# Abstract
+
+The OCI Runtime Specification aims to specify the inputs and outputs for running containers on various platforms.
+
+A container's input or configuration is specified as the `config.json` for the supported platforms and details fields that enable containers to run on that platform.
+It contains host specific information for the creation of a container.
+
+The outputs of a container are defined as both actions that can be performed on a container after it has been created and the environment details that the container provides to applications running inside of it.
+
 # Platforms
 
 Platforms defined by this specification are: