Added nerdtree preferences

prefs/nerdtree.vim

@@ -0,0 +1,9 @@
+" NERDTree shortcut
+map <C-n> :NERDTreeToggle<CR>
+
+" open a NERDTree automatically when vim starts up if no files were specified
+autocmd StdinReadPre * let s:std_in=1
+autocmd VimEnter * if argc() == 0 && !exists("s:std_in") | NERDTree | endif
+
+" close vim if the only window left open is a NERDTree
+autocmd bufenter * if (winnr("$") == 1 && exists("b:NERDTreeType") && b:NERDTreeType == "primary") | q | endif