How about:

```
The JSON encoder in Rails 4.1 no longer supports encoding BigDecimals as JSON numbers.
If your application depends on this, you should add the 'activesupport-json_encoder'
gem to your Gemfile to restore the old behavior, otherwise you can safely remove the 
related 'active_support.encode_big_decimal_as_string' configuration from your application.
```

So that we tell people what to do in all cases, wdyt?