add gravity+fetchXML description

[YuliyaPoznyak]

No description provided.

[georged]

@YuliyaPoznyak can we add twig variables to the filtering fetchxml? For example, getting contacts belonging to the same account as current user:

<filter>
  <condition attribute="parentaccountid" operator="eq" value="{{ user.record.parentaccount.Id }}" />
</filter>

Please test that scenario (ensure that user.record.parentaccount.Id actually returns the guid) and, if it works, expand the documentation to include twig.