Cloud identity docs

This PR adds the Cloud Identity service to our documentation. We need the following language samples:

- [x] Bash
- [ ] C#
- [x] Golang
- [ ] Java
- [ ] Javascript
- [x] PHP
- [ ] Python
- [x] Ruby
I see what you mean. I chose to use the conditional because the _Update user_ section mentions that if you don't know what a user's ID is, you can list all users and find it by querying usernames. Then again, this is a pretty obvious thing to do - so I don't think users will benefit from seeing it. I'll change it.