Sound Classifier need "Advanced Usage" user guide page

[TobyRoseman]

With the 5.5 release the sounds classifier will have:

• A way of reusing deep feature across training (Sound Classifier needs way to save/use deep features #1601)
• A way to control the custom neural network (Sound Classifier Should Allow Tuning the Structure of the Custom Neural Network #1477). Two layers of 100 units each will continue to be the default.

We need an advanced section of the user guide which explains each of these features in more detail and gives example code.

[coolioxlr]

+1

[TobyRoseman]

Done by #1722