add missing method identifier in docs
add missing method identifier in docs

shoyer/xarray,shoyer/xarray,shoyer/xray,xray/xray,pydata/xarray,chunweiyuan/xarray,jhamman/xray,jhamman/xarray,markelg/xray,jhamman/xarray,jcmgray/xarray,markelg/xray,pydata/xarray,jhamman/xarray,pydata/xarray,rabernat/xray,rabernat/xray,markelg/xray