README.md in sinatra-exstatic-assets-3.0.0 vs README.md in sinatra-exstatic-assets-3.1.0

@@ -83,9 +83,25 @@
             = img "http://www.flickr.com/photos/redfernneil/1317915651/", width: 500, height: 250, alt: "Something about the photo"
 
 
 There is also more detailed documentation on each helper in the {Sinatra::Exstatic::Helpers} API docs.
 
+## Formats ##
+
+The time format is the result of the file's `mtime`. If you wish for a different kind of format, SHA1 of the file is available (and I may add more). To use:
+
+      require 'sinatra/exstatic_assets/formats'
+      register Sinatra::Exstatic
+
+      configure do
+        set :timestamp_format, :sha1
+      end
+
+And now the value returned will be the SHA1 hash of the file. You can override the choice by passing the `timestamp_format` to the method:
+
+      = css_tag "/css/screen.css", timestamp_format: :mtime
+
+
 ### TODO ###
 
 * Make it easy to pass in caching options.
 * Default dirs set up for things like /css, /images etc.
 * An image link tag.
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