Documented collection metadata feature.

Readme.md

@@ -19,7 +19,7 @@ There are two ways to create collections:
 
   - **by pattern** - this is just passing a globing pattern that will group any files that match into the same collection.
   - **by metadata** - this is adding a specific `collection` metadata field to each item that you want to add to a collection.
-  
+
 The simplest way to create a collection is to use a pattern to match the files you want to group together:
 
 ```js
@@ -64,6 +64,33 @@ My article contents...
 
 All of the files with a matching `collection` will be added to an array that is exposed as a key of the same name on the global Metalsmith `metadata`.
 
+Additional metadata can be added to the collection object.
+
+```js
+metalsmith.use(collections({
+  articles: {
+    sortBy: 'date',
+    reverse: true,
+    metadata: {
+        name: 'Articles',
+        description: 'The Articles listed here...'
+    }
+  }
+}));
+```
+
+Collection metadata can also be assigned from a `json` or `yaml` file.
+
+```js
+metalsmith.use(collections({
+  articles: {
+    sortBy: 'date',
+    reverse: true,
+    metadata: 'path/to/file.json'
+  }
+}));
+```
+
 ## CLI Usage
 
 All of the same options apply, just add them to the `"plugins"` key in your `metalsmith.json` configuration: