Most people don't care about the source code, but we have a huge link to the setup guide [1] (and there is a link to GitHub in the footer).
Also I'm not sure where you bring the "but it doesn't receive bug fixes" statement from? We have a documented upgrade process [2] for the images you create using our documented setup guide.
[1] https://redash.io/help-onpremise/setup/setting-up-redash-ins... [2] https://redash.io/help-onpremise/maintenance/how-to-upgrade-...