Update readme with spec (devcontainers#36)

Author: bamurtaugh

README.md

@@ -6,9 +6,17 @@ A development container allows you to use a container as a full-featured develop
 
 The Development Containers Specification seeks to find ways to enrich existing formats with common development specific settings, tools, and configuration while still providing a simplified, un-orchestrated single container option – so that they can be used as coding environments or for continuous integration and testing.
 
+![Stages of container-based development, from development to deployment](images/dev-container-stages.png)
+
 The first format in the specification, devcontainer.json, was born out of necessity. It is a structured JSON with Comments (jsonc) metadata format that tools can use to store any needed configuration required to develop inside of local or cloud-based containerized coding. While this metadata can be persisted in a devcontainer.json today, we envision that this same structured data can be embedded in images and other formats – all while retaining a common object model for consistent processing.
 
-Beyond repeatable setup, these same development containers provide consistency to avoid environment specific problems across developers and centralized build and test automation services. You will be able to use the [upcoming open-source CLI reference implementation](https://github.com/microsoft/dev-container-spec/issues/9) either directly or integrated into product experience to use the structured metadata to deliver these benefits. It currently supports integrating with Docker Compose and a simplified, un-orchestrated single container option – so that they can be used as coding environments or for continuous integration and testing.
+Beyond repeatable setup, these same development containers provide consistency to avoid environment specific problems across developers and centralized build and test automation services. You will be able to use the [open-source CLI reference implementation](https://github.com/microsoft/dev-container-spec/issues/9) either directly or integrated into product experience to use the structured metadata to deliver these benefits. It currently supports integrating with Docker Compose and a simplified, un-orchestrated single container option – so that they can be used as coding environments or for continuous integration and testing.
+
+### Spec content
+
+You may review the specification in the [specs folder](https://github.com/devcontainers/spec/tree/main/docs/specs) of this repo.
+
+You may also review proposed references in the [proposals folder](https://github.com/devcontainers/spec/tree/main/proposals).
 
 ## Contributing and Feedback