Document what needs to be configured for an attribute to be available for projection

When we query something using containing grouping and aggregation functions we receive the exception bellow:

org.infinispan.objectfilter.ParsingException: ISPN014021: Queries containing grouping and aggregation functions must use projections.

The code used to receive this exception:

Query q = createQueryFromString("select count(u.something) from  User u where user.name = 'John' Group By u.name");

setProjections on QueryBuilder is deprecated and the information about how to use Projections using Query String is missing...

Also there is a TODO in http://infinispan.org/docs/stable/user_guide/user_guide.html#projections