Reinstate and Update FAQ page

[fmbenhassine]

The FAQ page is outdated. Moreover, this page is not accessible from the project's main page or reference documentation or README. This page should be updated and made accessible from one of these resources.

EDIT: The FAQ section of Spring Data is part of the reference documentation: https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#faq.