Correct docker-compose demo docs

[reify-travis-brown]

Security is enabled by default so setting this environment variable has no effect unless the intent is to disable it for demo purposes.

Description

This change allows for a demo to be started without additional security setup. Without this change, the current instructions lead to an invalid security state that cannot be used until further security configuration is completed.

Issues Resolved

N/A

Checklist

• [x] By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and subject to the Developers Certificate of Origin. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[hdhalter]

Thanks, @reify-travis-brown !

@scrawfor99, @peterzhuamazon - Can you approve for technical accuracy? Thanks!