Document how to start with docker run

[rakyll]

The examples and documentation is not mentioning how to start the collector with the docker run command. Add a section to https://github.com/aws-observability/aws-otel-collector/blob/main/docs/developers/docker-demo.md before the demo to document how to start the collector with the right configuration.

[mxiamxia]

Added a section for starting the collector with docker run. It will bring up the collector with the default config.
https://github.com/aws-observability/aws-otel-collector/blob/main/docs/developers/docker-demo.md#run-a-single-aws-otel-collector-instance-in-docker