qga: update docs with systemd suspend support info

Commit 067927d62e ("qga: systemd hibernate/suspend/hybrid-sleep
support") failed to update qapi-schema.json after adding systemd
hibernate/suspend/hybrid-sleep capabilities to guest-suspend-* QGA
commands.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/qapi-schema.json

@@ -532,12 +532,12 @@
 #
 # Suspend guest to disk.
 #
-# This command tries to execute the scripts provided by the pm-utils package.
-# If it's not available, the suspend operation will be performed by manually
-# writing to a sysfs file.
+# This command attempts to suspend the guest using three strategies, in this
+# order:
 #
-# For the best results it's strongly recommended to have the pm-utils
-# package installed in the guest.
+# - systemd hibernate
+# - pm-utils (via pm-hibernate)
+# - manual write into sysfs
 #
 # This command does NOT return a response on success. There is a high chance
 # the command succeeded if the VM exits with a zero exit status or, when
@@ -560,12 +560,12 @@
 #
 # Suspend guest to ram.
 #
-# This command tries to execute the scripts provided by the pm-utils package.
-# If it's not available, the suspend operation will be performed by manually
-# writing to a sysfs file.
+# This command attempts to suspend the guest using three strategies, in this
+# order:
 #
-# For the best results it's strongly recommended to have the pm-utils
-# package installed in the guest.
+# - systemd suspend
+# - pm-utils (via pm-suspend)
+# - manual write into sysfs
 #
 # IMPORTANT: guest-suspend-ram requires working wakeup support in
 # QEMU. You should check QMP command query-current-machine returns
@@ -594,7 +594,10 @@
 #
 # Save guest state to disk and suspend to ram.
 #
-# This command requires the pm-utils package to be installed in the guest.
+# This command attempts to suspend the guest by executing, in this order:
+#
+# - systemd hybrid-sleep
+# - pm-utils (via pm-suspend-hybrid)
 #
 # IMPORTANT: guest-suspend-hybrid requires working wakeup support in
 # QEMU. You should check QMP command query-current-machine returns