Location and description of import_map.json

[k35o]

.vscode/import_map.json is used in deno.json as well as .vscode/settings.json. If deno.json uses it, I thought it was fine to place it in root.

Even if not, I felt that the following notations should be eliminated.

  "scopes": {
    "THIS FILE EXISTS ONLY FOR VSCODE! IT IS NOT USED AT RUNTIME": {}
  },

https://github.com/denoland/fresh/blob/main/.vscode/import_map.json#L2-L4