Merge pull request #195 from NOAA-GFDL/191.UpdateDocs

 Adding catalog documentation

docs/subtools.rst

@@ -7,6 +7,29 @@ fre app
 fre catalog
 --------
 
+The fre catalog tool brings the functionality of the `GFDL catalog builder <https://github.com/NOAA-GFDL/CatalogBuilder/tree/main>`_ to fre users. The catalog builder is a python community package ecosystem that allows you to generate data catalogs compatible with intake-esm.
+
+**Subtools**
+
+Buildcatalog - Generate a data catalog
+
+Validate - Validate the catalog
+
+**Flags**
+
+Overwrite - Overwrite an existing catalog at the given output path
+
+Apend - Append (without headerlist) to an existing catalog at the given output path
+
+**Quickstart**
+
+Catalogs are generated by the following command: fre catalog buildcatalog <INPUT_PATH> <OUTPUT_PATH>
+
+(OUTPUT_PATH should end with the desired output filename WITHOUT a file ending) See example below.
+
+.. code-block:: terminal
+fre catalog buildcatalog --overwrite /archive/path_to_data_dir ~/output
+
 fre check (not yet implemented)
 --------