Modify the "automatic installation" so it uses $XDG_CONFIG_HOME

[pepoluan]

I suggest replacing the following snippet in the Automatic Installation section on the Tips page:

let data_dir = has('nvim') ? stdpath('data') . '/site' : '~/.vim'

With the following:

if !empty($VIM_CONFIG_DIR)
    let data_dir = $VIM_CONFIG_DIR
elseif has('nvim')
    let data_dir = stdpath('data') . '/site'
elseif !empty($XDG_CONFIG_HOME)
    let data_dir = $XDG_CONFIG_HOME
else
    let data_dir = $HOME . '/.config/vim'
endif

It's not only easier to read, it is now compliant with XDG Base Directory Specification, but allowing override by setting the VIM_CONFIG_DIR env var.