Add vim 8 package manager instructions (elixir-editors#449)

See the following links for details: http://vimhelp.appspot.com/repeat.txt.html#packages https://shapeshed.com/vim-packages/

Author: lukebakken

README.md

@@ -16,6 +16,12 @@ Features:
 
 ### Plugin Managers
 
+```bash
+# vim 8 native package loading
+# http://vimhelp.appspot.com/repeat.txt.html#packages
+git clone https://github.com/elixir-lang/vim-elixir.git ~/.vim/pack/my-packages/start
+```
+
 ```bash
 # pathogen
 git clone https://github.com/elixir-lang/vim-elixir.git ~/.vim/bundle/vim-elixir