Update init.vim to support updated Vundle location

Before I noticed the rtp variable, the Vundle installation was a bit
nebulous to me.

TODO: Consider dropping support for vanilla altogether.

.gitignore

@@ -13,3 +13,4 @@
 **/*/.emacs.d/network-security.data
 **/*/.emacs.d/smex-items
 nvim/.netrwhist
+Vundle.vim

configs/shared/misc/.config/nvim/init.vim

@@ -3,7 +3,9 @@ set nocompatible              " be iMproved, required
 filetype off                  " required
 
 " set the runtime path to include Vundle and initialize
+" share Vundle between vim and neovim
 set rtp+=~/.vim/bundle/Vundle.vim
+set rtp+=~/.config/nvim/bundle/Vundle.vim
 call vundle#begin()
 " alternatively, pass a path where Vundle should install plugins
 "call vundle#begin('~/some/path/here')