Clarify Database setup

Clarify that the introductory paragraph is not the complete instruction
but more is to come to avoid confusion.

Change-Id: I273f6dd23414ec1f5d0aec30be8e0b50e51ea108
Closes-Bug: #1341172
Add Telemetry Alarming content

Add content describing the Telemetry Alarming feature
to the Admin guide.

Implements: blueprint add-ceilometer-admin-guide-to-openstack-manuals
Change-Id: I6a5364ef75564c40c4d893307d202a229ee528bd
Merge "Add Telemetry Alarming content"
Merge "Clarify Database setup"