grid and meta docstrings

cc @theengineear @etpinard 
i'm indifferent. it's nice since it will error as a positional argument sooner. the only downside is possible confusion with the get_figure(file_id_or_url) or whatever that signature. Just commenting it's a file_id or url there and a *grid* or grid_url. But yeah, in general, i think i like `grid_or_grid_url` +1