Compute nodes installation guide the lack of placement configuration section that lead to computing services start-up failure in the Ocata version

Compute nodes installation guide the lack of placement configuration section that lead to computing services start-up failure in the Ocata version

version ： ocata
Operation document location ：
https://github.com/openstack/openstack-manuals/blob/master/doc/install-guide/source/nova-compute-install.rst
Operation steps：
According to the document operation, to increase the compute nodes to environment, start computing services
Services to start the computation error
Log as follows：

2017-02-28 11:38:32.480 9517 ERROR oslo_service.service [-] Error starting thread.
2017-02-28 11:38:32.480 9517 ERROR oslo_service.service Traceback (most recent call last):
2017-02-28 11:38:32.480 9517 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/oslo_service/service.py", line 722, in run_service
2017-02-28 11:38:32.480 9517 ERROR oslo_service.service service.start()
2017-02-28 11:38:32.480 9517 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/nova/service.py", line 144, in start
2017-02-28 11:38:32.480 9517 ERROR oslo_service.service self.manager.init_host()
2017-02-28 11:38:32.480 9517 ERROR oslo_service.service File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 1136, in init_host
2017-02-28 11:38:32.480 9517 ERROR oslo_service.service raise exception.PlacementNotConfigured()
2017-02-28 11:38:32.480 9517 ERROR oslo_service.service Placeme