Update Readme to reflect external data

README.md

@@ -21,9 +21,11 @@ RTE computes fluxes given spectrally-resolved optical descriptions and source fu
 1. Set environment variables `FC` (the Fortran 2003 compiler) and `FCFLAGS` (compiler flags). Examples are provided in the `Compiler-flags.md` file.
 2. Set environment variables `RRTMGP_ROOT` to the top-level RTE+RRTMGP directory and `RTE_KERNELS` to `accel` if you want the OpenACC/OpenMP kernels rather than the default.
 3. `make libs` in the top-level directory will make the RTE and RRTMGP libraries.
-4. The examples and testing codes use netCDF. Set the variables `NCHOME` and `NFHOME` to the roots of the C and Fortran netCDF installations, then `make tests` to build and run these. (A few files need to be downloaded for `examples/rfmip-clear-sky`. The default is to download these with `wget` but a Python script is also available.)
-5. Evaluating the results of the tests requires `Python` and the packages described in `environment.yml`. Comparisons can be made with `make check` in the top level directory.
-6. `make` invoked without a target in the top level attempts all three steps.
+4. The examples and testing codes use netCDF. Set the variables `NCHOME` and `NFHOME` to the roots of the C and Fortran netCDF installations. 
+5. Download the RRTMGP data either by cloning the [data repository](https://github.com/earth-system-radiation/rrtmgp-data) or from the [Zenodo archive](https://doi.org/10.5281/zenodo.7988260). Set the environment variable `RRTMGP_DATA` to the root of this directory. 
+6. `make tests` to will build and run the test. 
+7. Evaluating the results of the tests requires `Python` and the packages described in `environment.yml`. Comparisons can be made with `make check` in the top level directory. 
+8. `make` invoked without a target in the top level attempts all three steps.
 
 ## Examples