This is the development code of Nvim-R. Stable versions of this plugin are released at http://www.lepem.ufc.br/jaa/NvimR.html.
If you use a plugin manager, such as vim-plug, Vundle or Pathogen, follow its instructions on how to install plugins from github. The plugin manager will set the value of 'runtimepath' for you, and you can check it with the following command:
:set runtimepath?If you do not use a plugin manager, you should clone this directory wherever you want and manually adjust Neovim's runtimepath in your ~/.config/nvim/init.vim as in the example below:
set runtimepath=~/Nvim-R,~/.config/nvim,$VIMRUNTIME,~/.config/nvim/after
To use this version, you will also need the development version of nvimcom.
Please, read the file doc/Nvim-R.txt for usage details.