Clearly document transaction integration patterns for repository classes

I was implementing Data on top of WildFly 9 today. After about an hour of battling I got it to work end to end. In my case I was using a REST API, but used these steps:

• Annotate the outermost layer with @javax.transactional.Transactional
• Set the transaction strategy to container managed (Separate JIRA ticket coming for this pain)

Only then did saves work properly for the repository interface.