Issue #16241: document -X faulthandler command line option.

Patch by Marek Ć uppa.
diff --git a/Doc/using/cmdline.rst b/Doc/using/cmdline.rst
index dbe6c47..2703684 100644
--- a/Doc/using/cmdline.rst
+++ b/Doc/using/cmdline.rst
@@ -358,7 +358,8 @@
 .. cmdoption:: -X
 
    Reserved for various implementation-specific options.  CPython currently
-   defines none of them, but allows to pass arbitrary values and retrieve
+   defines just one, you can use ``-X faulthander`` to enable
+   :data:`faulthandler`. It also allows to pass arbitrary values and retrieve
    them through the :data:`sys._xoptions` dictionary.
 
    .. versionchanged:: 3.2
diff --git a/Misc/ACKS b/Misc/ACKS
index 808d1ba..f01619e 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1133,6 +1133,7 @@
 Nathan Sullivan
 Mark Summerfield
 Reuben Sumner
+Marek Šuppa
 Hisao Suzuki
 Kalle Svensson
 Andrew Svetlov