Add javadoc to Fill.java.

Explain the `tf.fill()` function.

Author: khatchad

com.ibm.wala.cast.python.ml/source/com/ibm/wala/cast/python/ml/client/Fill.java

@@ -10,6 +10,9 @@
 /**
  * A representation of the TensorFlow <code>fill()</code> function.
  *
+ * <p>The fill() function creates a new tensor with a specified shape and fills it with a specified
+ * value.
+ *
  * @see <a href="https://www.tensorflow.org/api_docs/python/tf/fill">TensorFlow fill() API</a>.
  * @author <a href="mailto:[email protected]">Raffi Khatchadourian</a>
  */