[olympic/developer-handbook] Elaborate more on exception usage

developer-handbook.md

@@ -177,6 +177,9 @@ Instead of throwing exceptions, all engine code should return
 For the sake of consistency, try to stick to ```ox::Error``` in non-engine code
 as well, but non-engine code is free to use exceptions when they make sense.
 
+Exceptions should generally just use ```OxException```, which is bascially an
+exception form of ```ox::Error```.
+
 ### File I/O
 
 All engine file I/O should go through Keel, which should go through