Add codespace "blueprint"

Aka `devcontainer.json` file so everyone else will get machine with
`go` and `terraform` preinstalled.

.devcontainer/devcontainer.json

@@ -0,0 +1,13 @@
+{
+	"image": "mcr.microsoft.com/devcontainers/universal:2",
+	"features": {
+		"ghcr.io/devcontainers-contrib/features/terraform-asdf:2": {}
+	},
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"golang.go"
+			]
+		}
+	}
+}

docs/contributing/README.md

@@ -5,7 +5,6 @@ Either:
 - [Devbox](https://www.jetpack.io/devbox/docs/installing_devbox/) for dependencies and development
 - install dependencies manually, see [Requirements](../../README.md).
 - GitHub's Codespaces which comes with `go` preinstalled out of the box
-    - you'll need to install Terraform via `sudo apt update && sudo apt install terraform` and run tunnel to your Django (dev.sleuth.io) server locally
     - to run in Codespaces open this repo on GitHub, find green `<> Code` dropdown button and select `Codespaces` tab
 
 ## Getting dependencies