add security section to rizzo docs

security section for rizzo docs
Yes, when accessing an external service, it's best, when possible, to route that through your app's back end.  The credentials can be stored in memory, accessed from the OS environment variables, or parsed from a specific file.

Some possible pseudo code

Front-end call
```
$.ajax({
  url: "http://mydomain.com/widgets",
  method: "GET",
  accepts: "contentType: "application/json",
  authToken: "server-generated-auto-token"
  ...
});
```

Back end call
```
uri = URI('http://otherservice.com/widgets?accessToken=' + ENV["ACCESS_TOKEN"])
res = Net::HTTP.get_response(uri)
// Send response to client
```