add text about no order

Author: Andy Barrett

notebooks/SMAP/README.md

@@ -6,6 +6,8 @@ This set of three tutorials demonstrates how to search for, download and plot SM
 
 We use the [SMAP L3 Radiometer Global Daily 36 km EASE-Grid Soil Moisture, Version 8](https://nsidc.org/data/SPL3SMP/versions/9) data set as an example.
 
+All notebooks are self contained, so there is no particular order to run them.  However, [working_with_smap_data_in_xarray](notebooks/SMAP/working_with_smap_in_xarray.ipynb) provides the most basic introduction.
+
 [working_with_smap_data_in_xarray](notebooks/SMAP/working_with_smap_in_xarray.ipynb) demonstrates how to search for and download SMAP data using `earthaccess`, and how to load a single group into an `xarray.Dataset` using `open_dataset`.  It also shows how to add informative dimension names and geospatial coordinates to the dataset so that the data variables can be plotted and analyzed using the powerful `xarray` methods.
 
 [working_with_smap_as_datatree](notebooks/SMAP/working_with_smap_as_datatree.ipynb) demonstrates how to load the full SMAP datafile as an `xarray.Datatree`.  It also shows how to load a time series of SMAP files.