Proposal to readme: add startup instructions

[edmomot]

Having some trouble with git, otherwise I'd make a PR, but it would have helped me to have this information in the readme. Thanks for creating this image!

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Verify the docker image is running with: sudo ./openmanage.sh status

Open browser to OpenManage web page at https://localhost:1311

Use these credentials on the page to log in user: root pw: password