add PROJ_DEBUG levels

Author: jmckenna

en/optimization/debugging.txt

@@ -9,7 +9,7 @@
 
 :Author: Jeff McKenna
 :Contact: jmckenna at gatewaygeomatics.com
-:Last Updated: 2025-08-02
+:Last Updated: 2025-10-05
 
 .. contents:: Table of Contents
     :depth: 3
@@ -355,7 +355,26 @@ such as:
      END
    END
 
-.. NOTE::
+Since the PROJ 9.3.0 release, there are 4 levels that you can set to 
+increase the information returned from `PROJ_DEBUG`, such as:
+
+**Level 0**
+  No message (PROJ_DEBUG 0)
+  
+**Level 1**
+  Error messages only (PROJ_DEBUG 1)
+  
+**Level 2**
+  Same as level 1, but with debug messages.  Setting `"PROJ_DEBUG" "ON"` 
+  is an alias to this level 2.  (PROJ_DEBUG 2)
+  
+**Level 3**
+  Same as level 2, with verbose messages (PROJ_DEBUG 3)
+  
+**Level 4**
+  Same as level 3, with very verbose messages (PROJ_DEBUG 4)
+   
+.. TIP::
    You can set *"CPL_DEBUG" "PROJ"* to restrict the information returned to PROJ
    (and not GDAL in general)