add documentation for the file classifier cataloger config options

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

README.md

@@ -108,6 +108,17 @@ package:
     # same as -s ; SYFT_PACKAGE_CATALOGER_SCOPE env var
     scope: "squashed"
 
+# cataloging file classifications is exposed through the power-user subcommand
+file-classification:
+  cataloger:
+    # enable/disable cataloging of file classifications
+    # SYFT_FILE_CLASSIFICATION_CATALOGER_ENABLED env var
+    enabled: true
+
+    # the search space to look for file classifications (options: all-layers, squashed)
+    # SYFT_FILE_CLASSIFICATION_CATALOGER_SCOPE env var
+    scope: "squashed"
+
 # cataloging file metadata is exposed through the power-user subcommand
 file-metadata:
   cataloger: