[samples/java]: Add some more descriptive text to the README

Author: asimshankar

README.md

@@ -1,6 +1,16 @@
 # TensorFlow for Java: Examples
 
-Examples using the TensorFlow Java API.
+These examples include using pre-trained models for [image
+classification](label_image) and [object detection](object_detection),
+and driving the [training](training) of a pre-defined model - all using the
+TensorFlow Java APIs.
+
+The TensorFlow Java API does not have feature parity with the Python API.
+The Java APIs are most suitable for inference using pre-trained models
+and for training pre-defined models from a single Java process.
+
+However, Python will be the most convenient language for defining the
+numerical computation of a model.
 
 - [Slides](https://docs.google.com/presentation/d/e/2PACX-1vQ6DzxNTBrJo7K5P8t5_rBRGnyJoPUPBVOJR4ooHCwi4TlBFnIriFmI719rDNpcQzojqsV58aUqmBBx/pub?start=false&loop=false&delayms=3000) from January 2018.
 - See README.md in each subdirectory for details.