update docs

Author: oreoshake

README.md

@@ -49,6 +49,7 @@ This gem makes a few assumptions about how you will use some features.  For exam
   config.x_permitted_cross_domain_policies = 'none'
   config.csp = {
     :default_src => "https: self",
+    :enforce => proc {|controller| contoller.current_user.enforce_csp? }
     :frame_src => "https: http:.twimg.com http://itunes.apple.com",
     :img_src => "https:",
     :report_uri => '//example.com/uri-directive'