Merge branch 'readme-ver' into 'develop'

Update supported Debian /Ubuntu versions

See merge request ispconfig/ispconfig3!1893

Author: Till Brehm

README.md

@@ -26,8 +26,8 @@ Development branch: [![pipeline status](https://git.ispconfig.org/ispconfig/ispc
 [^1]: not actively tested
 
 ## Supported operating systems
-- Debian 9 - 11, and testing
-- Ubuntu 16.04 - 20.04
+- Debian 9 - 12, and testing
+- Ubuntu 16.04 - 22.04
 - CentOS 7 and 8
 
 ## Auto-install script