qemu-options: Add missing -iscsi Texinfo documentation

Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Max Reitz <mreitz@redhat.com>
Cc: qemu-block@nongnu.org
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <20171002140307.5292-6-armbru@redhat.com>
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: NRonnie Sahlberg <ronniesahlberg@gmail.com>

qemu-options.hx

@@ -1189,6 +1189,12 @@ DEF("iscsi", HAS_ARG, QEMU_OPTION_iscsi,
     "       [,timeout=timeout]\n"
     "                iSCSI session parameters\n", QEMU_ARCH_ALL)
 
+STEXI
+@item -iscsi
+@findex -iscsi
+Configure iSCSI session parameters.
+ETEXI
+
 STEXI
 @end table
 ETEXI