Rework exitOverride description (#2098)

* Rework exitOverride description

* Fix description to match implementation

* Tweak wording again

* Take out the first in case people think it is before displaying helper/error.

Readme.md

@@ -1094,8 +1094,9 @@ program.error('Custom processing has failed', { exitCode: 2, code: 'my.custom.er
 By default, Commander calls `process.exit` when it detects errors, or after displaying the help or version. You can override
 this behaviour and optionally supply a callback. The default override throws a `CommanderError`.
 
-The override callback is passed a `CommanderError` with properties `exitCode` number, `code` string, and `message`. The default override behaviour is to throw the error, except for async handling of executable subcommand completion which carries on. The normal display of error messages or version or help
-is not affected by the override which is called after the display.
+The override callback is passed a `CommanderError` with properties `exitCode` number, `code` string, and `message`.
+Commander expects the callback to terminate the normal program flow, and will call `process.exit` if the callback returns.
+The normal display of error messages or version or help is not affected by the override which is called after the display.
 
 ```js
 program.exitOverride();