doc: exitedAfterDisconnect value can be false

Fixed the documentation to reflect the changes in the default value
of worker.exitedAfterDisconnect

PR-URL: #29404
Fixes: #28837
Refs: #3743
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>

doc/api/cluster.md

@@ -336,7 +336,9 @@ added: v6.0.0
 
 * {boolean}
 
-Set by calling `.kill()` or `.disconnect()`. Until then, it is `undefined`.
+This property is `true` if the worker exited due to `.kill()` or
+`.disconnect()`. If the worker exited any other way, it is `false`. If the
+worker has not exited, it is `undefined`.
 
 The boolean [`worker.exitedAfterDisconnect`][] allows distinguishing between
 voluntary and accidental exit, the master may choose not to respawn a worker