Doc: clarify what's table name and how to change fields/indexes for QueryEntity/Annotations configs

Users got confused on:

• what should be a table name if SQL is configured with QueryEntity/Annotations
• how to add/remove columns if QueryEntity/Annotations were used for initial configurations

http://apache-ignite-users.70518.x6.nabble.com/query-on-BinaryObject-index-and-table-td19631.html