[DOCS] Add scatterplot matrix to classification example (#1539) (#1542)

Author: lcawl

docs/en/stack/ml/df-analytics/flightdata-classification.asciidoc

@@ -102,6 +102,7 @@ in {kib} or the {ref}/put-dfanalytics.html[create {dfanalytics-jobs}] API.
 
 [role="screenshot"]
 image::images/flights-classification-job-1.jpg["Creating a {dfanalytics-job} in {kib}"]
+--
 
 .. Choose `kibana_sample_data_flights` as the source index.
 .. Choose `classification` as the job type.
@@ -111,6 +112,23 @@ want to predict with the {classanalysis}.
 excluded fields. These fields will be excluded from the analysis. It is
 recommended to exclude fields that either contain erroneous data or describe the 
 `dependent_variable`.
++
+--
+The wizard includes a scatterplot matrix, which enables you to explore the 
+relationships between the numeric fields. The color of each point is affected by
+the value of the dependent variable for that document, as shown in the legend.
+You can use this matrix to help you decide which fields to include or exclude
+from the analysis.
+
+[role="screenshot"]
+image::images/flights-classification-scatterplot.png["A scatterplot matrix for three fields in {kib}"]
+
+If you want these charts to represent data from a larger sample size or from a
+randomized selection of documents, you can change the default behavior. However, 
+a larger sample size might slow down the performance of the matrix and a
+randomized selection might put more load on the cluster due to the more
+intensive query.
+--
 .. Choose a training percent of `10` which means it randomly selects 10% of the
 source data for training. While that value is low for this example, for many
 large data sets using a small training sample greatly reduces runtime without 
@@ -129,8 +147,8 @@ analysis. In {kib}, the index name matches the job ID by default. It will
 contain a copy of the source index data where each document is annotated with
 the results. If the index does not exist, it will be created automatically.
 .. Use default values for all other options.
-
-
++
+--
 .API example
 [%collapsible]
 ====