Update README.md

Update README.

README.md

@@ -1,4 +1,45 @@
 cornfig
 =======
 
-Apply configuration from cloud metadata
+Apply configuration from cloud metadata.
+
+
+## What does it do?
+
+it turns a cloud-metdata file like this:
+```
+{"config": {"keystone": {"database": {"host": "127.0.0.1", "user": "keystone", "password": "foobar"}}}}
+```
+into service config files like this:
+```
+[sql]
+connection = mysql://keystone:foobar@127.0.0.1/keystone
+...other settings...
+```
+
+## But HOW??
+
+Just pass it the path to a directory tree of templates:
+```
+cornfig /home/me/my_templates
+```
+
+## Templates?
+
+The template directory structure should mimic a root filesystem, and contain templates for only those files you want cornfig-ed.
+
+e.g.
+```
+~/my_templates$ tree
+.
+└── etc
+    ├── keystone
+    │   └── keystone.conf
+    └── mysql
+        └── mysql.conf
+```
+
+If a template is executable it will be treated as an *executable template*.
+Otherwise, it will be treated as a *moustache template*.
+
+