doc: Clarify virtiofsd requirements

Closes lxc#1702

Signed-off-by: Stéphane Graber <[email protected]>

Author: stgraber

doc/requirements.md

@@ -46,6 +46,8 @@ Both tools should be available in the user's `PATH`.
 
 For virtual machines, QEMU 6.0 or higher is required.
 
+When using `virtiofsd`, only the [Rust rewrite](https://gitlab.com/virtio-fs/virtiofsd) of `virtiofsd` is supported.
+
 ## Additional libraries (and development headers)
 
 Incus uses `cowsql` for its database, to build and set it up, you can