Activate notifications for the file with ID [file-id] by posting some JSON to this URL:
https://www.googleapis.com/drive/v3/files/[file-id]/watch
Authorization: Bearer auth_token_for_current_user
Content-Type: application/json
Minimal JSON you need to POST:
{
"id": "[some unique ID for your push, you can define it yourself but it mus be unique]",
"type": "web_hook",