migration: massage cpr-reboot documentation

Re-wrap the cpr-reboot documentation to 70 columns, use '@' for
cpr-reboot references, capitalize COLO and VFIO, and tweak the
wording.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Link: https://lore.kernel.org/r/1709218462-3640-1-git-send-email-steven.sistare@oracle.com
[peterx: s/qemu/QEMU per Markus's suggestion]
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>

qapi/migration.json

@@ -636,28 +636,30 @@
 #
 # @normal: the original form of migration. (since 8.2)
 #
-# @cpr-reboot: The migrate command stops the VM and saves state to the URI.
-#     After quitting qemu, the user resumes by running qemu -incoming.
-#
-#     This mode allows the user to quit qemu, and restart an updated version
-#     of qemu.  The user may even update and reboot the OS before restarting,
-#     as long as the URI persists across a reboot.
-#
-#     Unlike normal mode, the use of certain local storage options does not
-#     block the migration, but the user must not modify guest block devices
-#     between the quit and restart.
-#
-#     This mode supports vfio devices provided the user first puts the guest
-#     in the suspended runstate, such as by issuing guest-suspend-ram to the
-#     qemu guest agent.
-#
-#     Best performance is achieved when the memory backend is shared and the
-#     @x-ignore-shared migration capability is set, but this is not required.
-#     Further, if the user reboots before restarting such a configuration, the
-#     shared backend must be be non-volatile across reboot, such as by backing
-#     it with a dax device.
-#
-#     cpr-reboot may not be used with postcopy, colo, or background-snapshot.
+# @cpr-reboot: The migrate command stops the VM and saves state to
+#     the URI.  After quitting QEMU, the user resumes by running
+#     QEMU -incoming.
+#
+#     This mode allows the user to quit QEMU, optionally update and
+#     reboot the OS, and restart QEMU.  If the user reboots, the URI
+#     must persist across the reboot, such as by using a file.
+#
+#     Unlike normal mode, the use of certain local storage options
+#     does not block the migration, but the user must not modify the
+#     contents of guest block devices between the quit and restart.
+#
+#     This mode supports VFIO devices provided the user first puts
+#     the guest in the suspended runstate, such as by issuing
+#     guest-suspend-ram to the QEMU guest agent.
+#
+#     Best performance is achieved when the memory backend is shared
+#     and the @x-ignore-shared migration capability is set, but this
+#     is not required.  Further, if the user reboots before restarting
+#     such a configuration, the shared memory must persist across the
+#     reboot, such as by backing it with a dax device.
+#
+#     @cpr-reboot may not be used with postcopy, background-snapshot,
+#     or COLO.
 #
 #     (since 8.2)
 ##