Example get descriptors value from text search

[xavierfav]

The example test.html shows how to retrieve sound from a text query. Moreover, it provides a way to then get the analysis of the retrieved sounds by performing another request.
However, the example does not show how to get analysis descriptors from text search request directly.

To make people more aware of the API good uses, it would be useful to have an example of how to perform a text query and specify some descriptors to be retrieved.

I plan to add a descriptors parameter in the example 2 of the test.html.