Update readme

README.md

@@ -185,7 +185,7 @@ $ crds sync --contexts roman-edit
 The CRDS_READONLY_CACHE variable should not be set, since references will need to be downloaded to your local cache as
 they are requested.
 
-Additionally, currently WebbPSF data is also required. Follow [these instructions to download the data files / point to existing files on the shared internal network](https://webbpsf.readthedocs.io/en/latest/installation.html#data-install).
+> **NOTE:** If it is desired to run tests against WebbPSF data, use the `pytest --webbpsf` flag or the `-webbpsf` tox factor and follow [these instructions to download the data files / point to existing files on the shared internal network](https://webbpsf.readthedocs.io/en/latest/installation.html#data-install).
 
 ### Running tests