Add support for devcontainers.

.devcontainer/devcontainer.json

@@ -0,0 +1,32 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/debian
+{
+    "name": "QMK CLI",
+    // Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
+    "image": "ghcr.io/qmk/qmk_cli",
+    "customizations": {
+        "vscode": {
+            "extensions": [
+                "amodio.toggle-excluded-files",
+                "EditorConfig.EditorConfig",
+                "xaver.clang-format",
+                "llvm-vs-code-extensions.vscode-clangd",
+                "bierner.github-markdown-preview",
+                "donjayamanne.git-extension-pack"
+            ]
+        }
+    },
+    "postCreateCommand": "/workspaces/qmk_userspace/.devcontainer/setup.sh"
+
+    // Features to add to the dev container. More info: https://containers.dev/features.
+    // "features": {},
+
+    // Use 'forwardPorts' to make a list of ports inside the container available locally.
+    // "forwardPorts": [],
+
+    // Configure tool-specific properties.
+    // "customizations": {},
+
+    // Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+    // "remoteUser": "root"
+}

.devcontainer/setup.sh

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+#!/usr/bin/env bash
+
+set -eEuo pipefail
+
+wget https://bootstrap.pypa.io/get-pip.py
+python3 get-pip.py
+python3 -m pip install qmk
+rm get-pip.py
+
+python3 -m pip install --upgrade milc
+
+git config --global --add safe.directory /workspaces/qmk_userspace
+git submodule update --init --recursive
+
+[ -d /workspaces/qmk_firmware ] || git clone https://github.com/qmk/qmk_firmware.git /workspaces/qmk_firmware
+git config --global --add safe.directory /workspaces/qmk_firmware
+
+qmk config user.qmk_home=/workspaces/qmk_firmware
+qmk config user.overlay_dir=/workspaces/qmk_userspace
+
+qmk git-submodule

.vscode/extensions.json

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+// Suggested extensions
+{
+  "recommendations": [
+    "amodio.toggle-excluded-files",
+    "EditorConfig.EditorConfig",
+    "xaver.clang-format",
+    "llvm-vs-code-extensions.vscode-clangd",
+    "bierner.github-markdown-preview",
+    "donjayamanne.git-extension-pack"
+  ]
+}