README: link to additional options for :truncation is broken

[dmolesUC]

Under "What strategy is fastest?", the README says:

If you are using ActiveRecord then take a look at the additional options available for :truncation.

However, there is no "Additional ActiveRecord options for Truncation" section. It appears to have been removed after 1.7.0.

[dmolesUC]

Actually, it looks like it was moved to the ActiveRecord-specific README.