efi: add API doc entry for ovmf_debug_log

Document the newly added sysfs ABI for accessing the in-memory debug log
provided by OVMF EFI firmware (when enabled)

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Author: kraxel

Documentation/ABI/testing/sysfs-firmware-efi

@@ -36,3 +36,10 @@ Description:	Displays the content of the Runtime Configuration Interface
 		Table version 2 on Dell EMC PowerEdge systems in binary format
 Users:		It is used by Dell EMC OpenManage Server Administrator tool to
 		populate BIOS setup page.
+
+What:		/sys/firmware/efi/ovmf_debug_log
+Date:		July 2025
+Contact:	Gerd Hoffmann <kraxel@redhat.com>, linux-efi@vger.kernel.org
+Description:	Displays the content of the OVMF debug log buffer.  The file is
+		only present in case the firmware supports logging to a memory
+		buffer.