Update VS Code project mtime

This makes it easier to find a recently-worked-on project in a list of directories.

Run command “Tasks: Open User Tasks”. Within the the array `“tasks”, add:

    {
      "label": "update project folder mtime",
      "type": "shell",
      "command": "touch .",
      "presentation": {
        "echo": true,
        "reveal": "silent",
        "focus": false,
        "panel": "shared",
        "showReuseMessage": false,
        "clear": false
      },
      "runOptions": {
        "runOn": "folderOpen"
      }
    }

This runs touch . within a project folder whenever it is opened in VS Code.