docs: add a note that spice channel is usable only with spice graphics
docs: add a note that spice channel is usable only with spice graphics

To prevent a confusion about missing chardev argument in qemu
command line add a note about that behavior into documentation.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1129198

Signed-off-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>

jfehlig/libvirt,eskultety/libvirt,jardasgit/libvirt,andreabolognani/libvirt,agx/libvirt,taget/libvirt,taget/libvirt,crobinso/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,olafhering/libvirt,eskultety/libvirt,VenkatDatta/libvirt,eskultety/libvirt,jardasgit/libvirt,jardasgit/libvirt,zippy2/libvirt,taget/libvirt,taget/libvirt,agx/libvirt,fabianfreyer/libvirt,crobinso/libvirt,andreabolognani/libvirt,rlaager/libvirt,olafhering/libvirt,jfehlig/libvirt,zippy2/libvirt,VenkatDatta/libvirt,taget/libvirt,zippy2/libvirt,datto/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,libvirt/libvirt,rlaager/libvirt,andreabolognani/libvirt,rlaager/libvirt,eskultety/libvirt,olafhering/libvirt,andreabolognani/libvirt,rlaager/libvirt,datto/libvirt,agx/libvirt,eskultety/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,jardasgit/libvirt,rlaager/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,andreabolognani/libvirt,nertpinx/libvirt,agx/libvirt,crobinso/libvirt,jardasgit/libvirt,zippy2/libvirt,agx/libvirt,crobinso/libvirt,datto/libvirt,olafhering/libvirt,libvirt/libvirt,libvirt/libvirt,datto/libvirt,libvirt/libvirt,datto/libvirt,nertpinx/libvirt