Checkout and create a link to the repository in your XDG_CONFIG_DIRECTORY on *nix or home directory on Windows. On *nix: ln -s $PWD ~/.config/vim. On Windows cmd /c mklink /J %USERPROFILE%\vimfiles $PWD.
vimrc is your vimrc (e.g. .vimrc, _vimrc, .vim/vimrc). You can rely on the behavior of Vim to pick it up for you if you've already linked the VIM directory in the previous step. Alternatively, you can create a link to it in your home directory. On *nix ln -s _vimrc ~/.vimrc, on Windows cmd /c mklink /h %USERPROFILE%\_vimrc _vimrc.
The vimrc configures Vim to conform to the XDG Base Directory specification. Although it's not necessary, the vimrc file can be placed in $XDG_CONFIG_HOME/vim, and Vim can be configured to read the vimrc from $XDG_CONFIG_HOME/vim/vimrc by setting VIMINIT:
XDG_VIMRC="${HOME}/.config/vim/vimrc"
if [ -f "$XDG_VIMRC" ]
then
export XDG_VIMRC
export VIMINIT='let $MYVIMRC="$XDG_VIMRC" | source $MYVIMRC'
fi