diff --git a/etc/accounts.yaml.sample b/etc/accounts.yaml.sample
index d191769..54fdcad 100644
--- a/etc/accounts.yaml.sample
+++ b/etc/accounts.yaml.sample
@@ -1,3 +1,7 @@
+# The number of accounts required can be estimated as CONCURRENCY x 2
+# Valid fields for credentials are defined in the descendants of
+# auth.Credentials - see KeystoneV[2|3]Credentials.CONF_ATTRIBUTES
+
 - username: 'user_1'
   tenant_name: 'test_tenant_1'
   password: 'test_password'