AAdd Rails helper to docs

README.md

@@ -56,6 +56,20 @@ end
 MyPage.new(title: "This is a PDF!").to_pdf
 ```
 
+### Rails integration
+
+To stream PDFs from Rails controllers, the `send_pdf` helper that wraps `send_data` and renders the PDF is available.
+
+```ruby
+class MyController < ApplicationController
+  include Phlex::PDF::Rails::Helpers
+
+  def show
+    send_pdf MyPage.new(title: "This is a PDF!")
+  end
+end
+```
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.