Added ubuntu 20.04 support + fixed minor font issue.

[geoai777]

Changes contain:

• zm built with Ubuntu 20.04 Focal image, 1.37 distribution latest;
• fix for "font not found" issue. Fixed css file provided;
• documentation on how to deploy image, sample docker-compose.yml file.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[connortechnology]

It is not clear to me why we need to patch skin.css. Seems that should be done upstream.

[geoai777]

In my case it was only way to fix fonts problem. Of course if upstream gets updated no patch is needed.