Also added reason why

GETTING-STARTED

@@ -13,8 +13,11 @@ edit settings.py as needed
 
 # Fill in data
 Visit https://nm.debian.org/am/db-export to download nm-mock.json; for privacy,
-sensitive information are replaced with mock strings. If you cannot login to
-the site, you can ask any DD to download it for you.
+sensitive information are replaced with mock strings.
+
+If you cannot login to the site, you can ask any DD to download it for you.
+There is nothing secret in the file, but I am afraid of giving out convenient
+email databases to anyone.
 
 ./manage.py import nm-mock.json