chore: update README.md

Author: johnstcn

README.md

@@ -2,6 +2,54 @@
 
 The `terraform-provider-envbuilder` is a Terraform provider that acts as a helper for setting up [`envbuilder`](https://envbuilder.sh) environments.
 
+It is used to determine if a pre-built image of a Devcontainer built from a given Git repository is present in a given Docker registry.
+If all layers that would result from building a particular devcontainer are present in the remote registry, then that image can simply be used as the starting point instead.
+
+## Usage
+
+Below is a very basic usage example. This checks a local registry running on port 5000 for an image built from the [Envbuilder Starter Devcontainer repo](https://github.com/coder/envbuilder-starter-devcontainer).
+
+```terraform
+terraform {
+  required_providers {
+    envbuilder = {
+      source = "coder/envbuilder"
+    }
+  }
+}
+
+resource "envbuilder_cached_image" "example" {
+  builder_image = "ghcr.io/coder/envbuilder:latest"
+  git_url       = "https://github.com/coder/envbuilder-starter-devcontainer"
+  cache_repo    = "localhost:5000"
+}
+
+output "builder_image" {
+  value = envbuilder_cached_image.example.builder_image
+}
+
+output "exists" {
+  value = envbuilder_cached_image.example.exists
+}
+
+output "id" {
+  value = envbuilder_cached_image.example.id
+}
+
+output "image" {
+  value = envbuilder_cached_image.example.image
+}
+
+```
+
+Take a look at [`envbuilder_cached_image_resource.tf`](./examples/resources/envbuilder_cached_image/envbuilder_cached_image_resource.tf) folder for a more detailed example.
+
+For use with [Coder](https://github.com/coder/coder), see the [Dev Containers documentation](https://coder.com/docs/templates/dev-containers) and check out the example templates:
+- [Docker](https://github.com/coder/coder/tree/main/examples/templates/devcontainer-docker)
+- [Kubernetes](https://github.com/coder/coder/tree/main/examples/templates/devcontainer-kuberntes)
+- [AWS VM](https://github.com/coder/coder/tree/main/examples/templates/devcontainer-aws-vm)
+- [GCP VM](https://github.com/coder/coder/tree/main/examples/templates/devcontainer-gcp-vm)
+
 ## Requirements
 
 - [Terraform](https://developer.hashicorp.com/terraform/downloads) >= 1.0

examples/provider/provider.tf

@@ -1 +1,32 @@
+terraform {
+  required_providers {
+    envbuilder = {
+      source = "coder/envbuilder"
+    }
+  }
+}
+
+// The provider currently requires no additional configuration.
 provider "envbuilder" {}
+
+resource "envbuilder_cached_image" "example" {
+  builder_image = "ghcr.io/coder/envbuilder:latest"
+  git_url       = "https://github.com/coder/envbuilder-starter-devcontainer"
+  cache_repo    = "localhost:5000"
+}
+
+output "builder_image" {
+  value = envbuilder_cached_image.example.builder_image
+}
+
+output "exists" {
+  value = envbuilder_cached_image.example.exists
+}
+
+output "id" {
+  value = envbuilder_cached_image.example.id
+}
+
+output "image" {
+  value = envbuilder_cached_image.example.image
+}