Add repo url to button

README.md

-[![Open in Coder](https://coder.development.infs.ch/open-in-coder.svg)](https://coder.development.infs.ch/templates/docker-code-server/workspace)
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+[![Open in Coder](https://coder.development.infs.ch/open-in-coder.svg)](https://coder.development.infs.ch/templates/docker-code-server/workspace?params.Git%20Repository%20HTTPS%20URL%3Dhttps%3A%2F%2Fgitlab.ost.ch%2Fdominic.klinger%2Fcoder-testworkspace.git)
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