gpart.8: add entry for xbootldr partition type

Reviewed by:	emaste, markj
Sponsored by:	The FreeBSD Foundation
Fixes:	dab8138e13 ("g_part,mkimg: Add additional GPT partition types")
Differential Revision:	https://reviews.freebsd.org/D56969

lib/geom/part/gpart.8

@@ -22,7 +22,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd May 9, 2026
+.Dd May 12, 2026
 .Dt GPART 8
 .Os
 .Sh NAME
@@ -1042,6 +1042,12 @@ A partition claimed by VMware VSAN.
 The scheme-specific type is
 .Qq Li "!381cfccc-7288-11e0-92ee-000c2911d0b2"
 for GPT.
+.It Cm xbootldr
+An Extended Boot Loader Partition (XBOOTLDR), secondary to the EFI system
+partition, used to store additional firmware or boot loader menu entries.
+The scheme-specific type is
+.Qq Li "!bc13c2ff-59e6-4262-a352-b275fd6f7172"
+for GPT.
 .El
 .Sh ATTRIBUTES
 The scheme-specific attributes for EBR: