Add CSV code to ease Custom Fields import.

[joaolucasmacedo]

Add the CSV code to ease required custom fields import:

name,content_types,label,group_name,type,Description,search_weight,filter_logic,ui_visibility,weight,choices
proxmox_id,virtualization.virtualmachine,Proxmox VM ID,ProxBox,integer,,1000,loose,read-write,100,
proxmox_keep_interface,dcim.interface,,ProxBox,boolean,,1000,loose,hidden,100,
proxmox_node,virtualization.virtualmachine,Proxmox Node,ProxBox,text,,1000,loose,read-write,100,
proxmox_type,virtualization.virtualmachine,Proxmox Type(VM or CT),ProxBox,select,,1000,loose,read-write,100,"['qemu', 'lxc']"