Update to indicate that isetbio is optional.

Still making it optional, but this seems to go pretty fast.

ExampleScenes/IsetbioExamples/README.md

+
 Isetbio Examples
 ==============
-The examples in this folder use RenderToolbox along with a separate toolbox called [isetbio](https://github.com/isetbio/isetbio).  You must have isetbio on your Matlab path for these to work.
+The examples in this folder use RenderToolbox.  If you have  a separate toolbox called [isetbio](https://github.com/isetbio/isetbio), installed, they will also bring the images into isetbio format and display them in an isetbio window.  You must have isetbio on your Matlab path for this latter feature  to work.
 
 If you use [ToolboxToolbox](https://github.com/ToolboxHub/ToolboxToolbox) then you can obtain RenderToolbox and isetbio and put them on your path like this:
 ```
@@ -10,6 +11,10 @@ tbUse('isetbio','reset','as-is');
 
 % Both at once
 tbUse({'RenderToolbox4', 'isetbio'});
+```
 
 Otherwise, you can follow the [installation](https://github.com/isetbio/isetbio/wiki/ISETBIO%20Installation) instructions on the isetbio wiki.
 
+It is worth a little thought about whether energy and quantal units are being handled properly on the conversion into isetbio.
+
+