DEV: improve comment explaining need for favicon proxy

app/controllers/static_controller.rb

@@ -103,12 +103,17 @@ class StaticController < ApplicationController
 
   FAVICON ||= -"favicon"
 
-  # We need to be able to draw our favicon on a canvas
-  # and pull it off the canvas into a data uri
-  # This can work by ensuring people set all the right CORS
-  # settings in the CDN asset, BUT its annoying and error prone
-  # instead we cache the favicon in redis and serve it out real quick with
-  # a huge expiry, we also cache these assets in nginx so it bypassed if needed
+  # We need to be able to draw our favicon on a canvas, this happens when you enable the feature
+  # that draws the notification count on top of favicon (per user default off)
+  #
+  # With s3 the original upload is going to be stored at s3, we don't have a local copy of the favicon.
+  # To allow canvas to work with s3 we are going to need to add special CORS headers and use
+  # a special crossorigin hint on the original, this is not easily workable.
+  #
+  # Forcing all consumers to set magic CORS headers on a CDN is also not workable for us.
+  #
+  # So we cache the favicon in redis and serve it out real quick with
+  # a huge expiry, we also cache these assets in nginx so it is bypassed if needed
   def favicon
     is_asset_path