right now, there are duplicate titles under contents --> guides
as shown in https://docs.openstack.org/devstack/latest/, although
they will forward to different pages, it is still a little confusing
for users. This change will hide toctree in guides.rst and users could
click links in page to jump to detail page to read more.
Change-Id: I2f3abeca7f56a3aedeabb48630ed2c61635b93cd