Add extension to a codespace.

Author: clifapps

.devcontainer/devcontainer.json

@@ -5,5 +5,19 @@
   "image": "mcr.microsoft.com/vscode/devcontainers/universal:latest",
 
   "remoteUser": "codespace",
-  "overrideCommand": false
+  "overrideCommand": false,
+
+  // Add the IDs of extensions you want installed when the container is created.
+  "customizations": {
+    "vscode": {
+        "extensions": [
+            "christian-kohler.path-intellisense"
+        ]
+    },
+    "codespaces": {
+        "openFiles": [
+            "codespace.md"
+        ]
+    }
+  }
 }