[ImageClassification Transfer Learning] - API documentation should provide more meaningful descriptions

Just to keep track of this. I understand we're in early preview and things can change, though. But since it is public preview, folks might review the reference in order to get any help.

For instance, the most "unknown parameters" for .NET developers have the following descriptions which don't "tell you anything":

[dnncatalog.imageclassification reference](https://docs.microsoft.com/en-us/dotnet/api/microsoft.ml.dnncatalog.imageclassification?view=ml-dotnet-preview#Microsoft_ML_DnnCatalog_ImageClassification_Microsoft_ML_ModelOperationsCatalog_System_String_System_String_System_String_System_String_System_String_System_String_Microsoft_ML_Transforms_DnnEstimator_Architecture_Microsoft_ML_Transforms_DnnEstimator_DnnFramework_System_Int32_System_Int32_System_Single_)

PARAMETER DESCRIPTIONS:
```
epoch
Int32
Number of training epochs.

batchSize
Int32
The batch size for training.

learningRate
Single
The learning rate for training.
```