Add comment JSON use

mathics_scanner/data/README.rst

@@ -7,3 +7,8 @@ Input data for conversion programs is in YAML:
 ``named-characters.yml`` and ``operators.yml`` Processed data is in
 JSON since that is the format which affords the fasted loading into
 Python programs (via ujson).
+
+Json output is not formatted in any way to facilitate loaded. To see
+json output formated use a JSON formatter like ``jq``:
+
+   cat characters.json | jq