qmp-commands: move 'migrate-start-postcopy' doc to schema

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

docs/qmp-commands.txt

@@ -456,16 +456,6 @@ Example:
 -> { "execute": "migrate-set-cache-size", "arguments": { "value": 536870912 } }
 <- { "return": {} }
 
-migrate-start-postcopy
-----------------------
-
-Switch an in-progress migration to postcopy mode. Ignored after the end of
-migration (or once already in postcopy).
-
-Example:
--> { "execute": "migrate-start-postcopy" }
-<- { "return": {} }
-
 query-migrate-cache-size
 ------------------------
 

qapi-schema.json

@@ -1079,6 +1079,12 @@
 # command.
 #
 # Since: 2.5
+#
+# Example:
+#
+# -> { "execute": "migrate-start-postcopy" }
+# <- { "return": {} }
+#
 ##
 { 'command': 'migrate-start-postcopy' }