Repo README (#53)

* Initial header for repo's readme

* more repo structure details, and placeholders

* Add usage section

* contributions

README.md

-# features
+# Development Container Features
+
+<table style="width: 100%; border-style: none;"><tr>
+<td style="width: 140px; text-align: center;"><a href="https://github.com/devcontainers"><img width="128px" src="https://raw.githubusercontent.com/microsoft/fluentui-system-icons/78c9587b995299d5bfc007a0077773556ecb0994/assets/Cube/SVG/ic_fluent_cube_32_filled.svg" alt="devcontainers organization logo"/></a></td>
+<td>
+<strong>Development Container 'Features'</strong><br />
+<i>A set of simple and reusable 'features'. Quickly add a language/tool/CLI to a development container.
+</td>
+</tr></table>
+
+'Features' are self-contained units of installation code and development container configuration. Features are designed to install atop a wide-range of base container images (**this repo focuses on `debian` based images**).
+
+Missing a CLI or language in your otherwise _perfect_ container image? Add the relevant 'feature' to the `features` property of a [`devcontainer.json`](https://containers.dev/implementors/json_reference/#general-properties).
+
+The [`devcontainer` CLI](https://github.com/devcontainers/cli), implemented by the VS Code Remote-Containers extension and Github Codespaces, is required to process a `devcontainer.json` and build a container images declaring 'features'.
+
+Development container 'features' are a [proposed](https://github.com/devcontainers/spec/blob/main/proposals/devcontainer-features.md) addition to the [development container specification](https://github.com/devcontainers/spec/blob/main/proposals/devcontainer-features.md). **Please note that 'features' are in preview and subject to breaking changes**.
 
 ## Repo Structure
 
@@ -7,7 +23,6 @@
 ├── lib
 │   └── utils.sh
 ├── README.md
-├── settings.env
 ├── src
 │   ├── dotnet
 │   │   ├── feature.json
@@ -15,9 +30,65 @@
 │   ├── go
 │   │   ├── feature.json
 │   │   └── install.sh
+|   ├── ...
+│   │   ├── feature.json
+│   │   └── install.sh
 ├── test
 │   ├── dotnet
 │   │   └── test.sh
 │   └── go
-│       └── test.sh
+│   |   └── test.sh
+|   ├── ...
+│   │   ├── feature.json
+│   │   └── install.sh
+├── test-scenarios
+│   ├── install_jupyterlab.sh
+│   ├── install_python_twice.sh
+|   ├── ...
+│   └── scenarios.json
+```
+
+- [`lib`](lib) - A collection of tools, scripts, and shared configuration used generally by this repo's features.
+- [`src`](src) - A collection of subfolders, each declaring a feature. Each subfolder contains at least a `feature.json` and the appropriately declared install script.
+- [`test`](test) - Mirroring `src`, a folder-per-feature with at least a `test.sh` script. The [`devcontainer` CLI](https://github.com/devcontainers/cli) will execute tests [of this form](https://github.com/devcontainers/features/blob/main/.github/workflows/test-all.yaml).
+- [`test-scenarios`](test-scenarios) - More complex scenarios involving a set of features from this repo. [`devcontainer` CLI](https://github.com/devcontainers/cli) will execute tests [of this form](https://github.com/devcontainers/features/blob/main/.github/workflows/test-scenarios.yaml).
+
+## Usage
+
+To reference a feature from this repository, add the desired features to a `devcontainer.json`.
+
+The example below installs the `go` and `docker-in-docker` declared in the [`./src`](./src) directory of this repository.
+
+See the relevant feature's README for supported options.
+
+```jsonc
+"image": "mcr.microsoft.com/devcontainers/base:ubuntu",  // Any generic, debian-based image.
+features: {
+    "devcontainers/features/go@latest": {
+        "version": "1.18"
+    },
+    "devcontainers/features/docker-in-docker@latest": {
+        "version": "latest",
+        "moby": true
+    }
+}
+```
+
+The `@latest` version annotation is added implicitly if omitted. To pin to a specific [release tag](https://github.com/devcontainers/features/releases), append it to the end of the feature.
+
+```jsonc
+features: {
+    "devcontainers/features/go@v0.0.2": {
+        "version": "1.18"
+    },
 ```
+
+## Contributions
+
+### Contibuting to this repository
+
+This repository will accept improvement and bug fix contributions related to the [current set of maintained features](./src).
+
+### Creating your own collection of features
+
+_More information your creating own set of features will be posted soon._