Configuration and example docs

README.md

@@ -1,3 +1,19 @@
 # Lumbar Long Expires
 
 Lumbar plugin that provides long-expires resource loading for lumbar modules.
+
+## Configuration
+
+To enable this plugin a `long-expires` key must be defined on the root lumbar config
+object. The value of this key is the process that is executed to generate expires
+cache busting key. This could be a unique id from source control such as the git
+commit sha, a timestamp, or any other value that will be unique on each build.
+
+## Example
+
+The following example uses the current git SHA as the unique token.
+
+    {
+      "modules": [],
+      "long-expires": "git rev-parse HEAD"
+    }