Update README.md

Update README.

README.md

@@ -4,7 +4,7 @@ cornfig
 Apply configuration from cloud metadata.
 
 
-## What does it do?
+# What does it do?
 
 it turns a cloud-metdata file like this:
 ```
@@ -17,14 +17,14 @@ connection = mysql://keystone:foobar@127.0.0.1/keystone
 ...other settings...
 ```
 
-## But HOW??
+# But HOW??
 
 Just pass it the path to a directory tree of templates:
 ```
 cornfig /home/me/my_templates
 ```
 
-## Templates?
+# Templates?
 
 The template directory structure should mimic a root filesystem, and contain templates for only those files you want cornfig-ed.
 
@@ -39,7 +39,30 @@ e.g.
         └── mysql.conf
 ```
 
-If a template is executable it will be treated as an *executable template*.
-Otherwise, it will be treated as a *moustache template*.
+If a template is executable it will be treated as an **executable template**.
+Otherwise, it will be treated as a **moustache template**.
+
+## Moustache Templates
+
+If you don't need any logic, just some string substitution, use a moustache template:
+
+```
+[sql]
+connection = mysql://{{keystone.database.user}}:{{keystone.database.password}@{{keystone.database.host}}/keystone
+```
+
+## Executable Templates
+
+An executable template is a script which accepts parameters in environment variables, and writes a config file to standard out.
+
+The output of the script will be written to the path corresponding to the executable template's path in the template tree.
+
+e.g.
+```
+#/bin/sh
+echo "[sql]"
+echo "connection = mysql://$keystone_database_user:$keystone_database_password@$keystone_database_user/keystone"
+```
+