Add description of the Source Discovery Tool

Author: troyraen

tutorials/spherex/spherex_sdt/README.md

@@ -1,6 +1,12 @@
 # __Source Discovery Tool__
 
 ## Overview
+
+The SPHEREx Source Discovery Tool is the Python package `spx_sdt` (included in this directory), which is used to discover and extract sources from SPHEREx Spectral Images and visualize their spectra.
+The notebook [](sdt_irsa.md) demonstrates how to use it.
+
+### Directory Contents
+
 - `spx_sdt`: package including functions to run notebook
   - SExtractor files
     - `default.conv`: Convolution mask used as detection filter.

tutorials/spherex/spherex_sdt/sdt_irsa.md

@@ -14,6 +14,8 @@ jupyter:
 
 # __SPHEREx Source Discovery Tool IRSA Demo__
 
+The SPHEREx Source Discovery Tool is the Python package `spx_sdt` (included in this directory), which is used to discover and extract sources from SPHEREx Spectral Images and visualize their spectra.
+This notebook demonstrates how to use it.
 
 ## 1. Learning Goals