OS: Ubuntu 18.04.3 LTS
I just installed neovim using sudo apt-get install neovim and added the folder and file ~/.config/nvim/vim.init. At this moment the file has no content, but when I open up nvim and type :PlugInstall I get error: E492: Not an editor command: PlugInstall. I am clueless, what is going wrong?
I think you are trying to use vim-plug without previously installing it.