Add metaformats to README

Author: angelogladding

README.md

@@ -82,10 +82,17 @@ a tree was 30 years ago, and the second best time to plant a tree is now.']}}]
 
 ## Extensions
 
+The following extensions can be invoked via keyword arguments to `parse()` and `Parser()`.
+
 ### `expose_dom`
 
 Use `expose_dom=True` to expose the DOM of embedded properties.
 
+### `metaformats`
+
+Use `metaformats=True` to include any [metaformats](https://microformats.org/wiki/metaformats)
+found.
+
 ## Advanced Usage
 
 `parse` is a convenience method that delegates to `Parser`. More sophisticated