diff --git a/README.md b/README.md
index 50e2627..327c664 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,11 @@
 # !! Rough notes for now, expand later.
 
 
-## Ansible layout/howto
+## Ansible layout
 
 * Global defaults in group_vars/all.yml
+** This is where env-vars should be converted to Ansible vars. It also acts as a required-env list.
+** The CF env is usually stored in /etc/atl. The script `bin/ansible-with-atl-env` will run Ansible with that environment set.
+* Runtime information about the EC2 environment can be injected by depending on
+  `aws_metadata` in a role's `meta/main.yml`.
 
diff --git a/group_vars/all.yml b/group_vars/all.yml
index e50f9b9..f6e0984 100644
--- a/group_vars/all.yml
+++ b/group_vars/all.yml
@@ -6,5 +6,5 @@ atl_shared_mountpoint: "/media/atl"
 
 #  The following are imports from the environment. These are generally
 #  set in /etc/atl by the CloudFormation template and sourced before
-#  Ansible is run.
+#  Ansible is run. See bin/ansible-with-atl-env for a convenient wrapper.
 atl_efs_id: "{{ lookup('env', 'ATL_EFS_ID') }}"