Remove unused usage section from readme:

kendocode · kendocode · commit 80b0a84a1e07 · 2018-06-19T17:56:08.000-05:00
diff --git a/README.md b/README.md
@@ -16,9 +16,6 @@ Or install it yourself as:
 
     $ gem install html5sortable-rails
 
-## Usage
-
-TODO: Write usage instructions here
 
 ## Development
 
