DOCSP-3475 - Adding missing images for customization pages

Author: jeff-allen-mongo

source/customize-charts/field-level-options.txt

@@ -16,6 +16,10 @@ Within the customization tab, you can modify how |charts| displays
 data fields in your visualization. The customization options
 available depend on the data type of the value you are customizing.
 
+.. figure:: /images/charts/field-level-custom.png
+   :figwidth: 251px
+   :alt: Field level customizations
+
 Field Label Override
 --------------------
 

source/customize-charts/general-customization.txt

@@ -16,6 +16,10 @@ General Customization Options
 visualization at a high level, rather than individual pieces of the
 visualization.
 
+.. figure:: /images/charts/general-custom.png
+   :figwidth: 251px
+   :alt: Field level customizations
+
 Show or Hide Data Markers on a Line Chart
 -----------------------------------------