Update Supported-host-operating-systems.md (#17661)

For the following bug: #12334

- Call out that, currently on Ubuntu, Fleet Desktop only supports
display number of `0`

Author: noahtalerman

docs/Using Fleet/Supported-host-operating-systems.md

@@ -1,5 +1,3 @@
-
-
 # Supported host operating systems
 
 Fleet supports the following operating system versions on hosts. 
@@ -27,6 +25,8 @@ The osquery installer generated for MacOS by `fleetctl package` does not include
 The osquery installer will run on Linux distributions where `glibc` is >= 2.2 (there is ongoing work to make osquery work with `glibc` 2.12+).
 If you aren't sure what version of `glibc` your distribution is using, [DistroWatch](https://distrowatch.com/) is a great resource. 
 
+> On Linux, Fleet Desktop only supports $DISPLAY `:0`.
+
 > Fedora, CentOS 8 and 9 require a [gnome extension](https://extensions.gnome.org/extension/615/appindicator-support/) and Google Chrome set to the default browser for Fleet Desktop.
 
 > The `fleetctl package` command is not supported on DISA-STIG distribution.