Make the vnc display feature as experimental

Signed-off-by: Anders F Björklund <[email protected]>

Author: afbjorklund

docs/experimental.md

@@ -5,3 +5,4 @@ The following features are experimental and subject to change:
 - `mountType: 9p`
 - `vmType: vz` and relevant configurations (`mountType: virtiofs`, `rosetta`, `[]networks.vzNAT`)
 - `arch: riscv64`
+- `video.display: vnc` and relevant configuration (`video.vnc.display`)