Add .devcontainer for GitHub codespaces (star-bnl#438)

GitHub just announced that they give users 60 free hours each month on
[Codespaces](https://github.com/codespaces)
Let's run our STAR software in the cloud 😺

Author: plexoos

.devcontainer/devcontainer.json

@@ -0,0 +1,4 @@
+{
+    "name": "star-sw",
+    "image": "ghcr.io/star-bnl/star-sw:latest"
+}