[PVE-User] Missing key info in Repository wiki

[Emmanuel Kasper]

Hi Eneko
> Just noticed the repository info wiki doesn't give information about apt
> keys:
> https://pve.proxmox.com/wiki/Package_Repositories
> 
> The following should be noted somewhere:
> 
> wget -O- "http://download.proxmox.com/debian/key.asc" | apt-key add -

https://pve.proxmox.com/wiki/Install_Proxmox_VE_on_Debian_Jessie
refers to this command because it is need when installing PVE from Debian

you actually need this command only when installing on top of debian,
since with an ISO installation the PVE apt key is installed with the
pve-manager package