How to document services

A service description for customers should try to answer the following FAQ:

What is the purpose of the service? What is its value for me?
What are limitations/restrictions/requirements/assumptions of the service?
Is there an example of another public project I can follow?
Is there an API? API Explorer link? How do I authenticate?
Can my internal project use the service? Does it implement ACLs?
Where is the documentation?
Where is the design doc?
How do I enable the service for my project? If by adding a config file to the project repo, what is the name of the config file and where is the documented .proto?
How do I provide feedback? How do I file bug for the service? What is the crbug label?
Who do I contact to if I have more questions?
Does it have SLA?