.vscode,README.md: add some development documentation

Author: raggi

.vscode/tasks.json

@@ -0,0 +1,20 @@
+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "Test Features",
+            "type": "shell",
+            "command": "npx @devcontainers/cli features test",
+            "group": {
+                "kind": "test",
+                "isDefault": true
+            },
+            "presentation": {
+                "reveal": "always",
+                "panel": "dedicated",
+                "clear": true
+            },
+            "problemMatcher": []
+        },
+    ]
+}

README.md

@@ -24,3 +24,16 @@ sudo tailscale up --accept-routes
 
 You'll only need to run `tailscale up` once per Codespace.
 The Tailscale state will be saved between rebuilds.
+
+## Development
+
+A convenient way to develop this feature is to use codespaces, as they start by
+default with many of the dependencies required (at least Docker and npx).
+
+Inside a codespace you can use the `Tasks:Run Test Task` command.
+
+On a standalone machine tests can be run with:
+
+```shell
+npx @devcontainers/cli features test
+```