VIM: Reinstall NERDTree

Nerdtree is a rather slow, but extremely useful plugin. So I made the
decission to reinstall it, but don't launch it on startup but with a
keybinding.

Signed-off-by: Tobias Manske <tobias.manske@mailbox.org>

vim/plugins/nerdtree/README.markdown

@@ -0,0 +1,96 @@
+The NERDTree
+=============
+
+Introduction
+------------
+
+The NERDTree is a file system explorer for the Vim editor. Using this plugin,
+users can visually browse complex directory hierarchies, quickly open files for
+reading or editing, and perform basic file system operations.
+
+This plugin can also be extended with custom mappings using a special API. The
+details of this API and of other NERDTree features are described in the
+included documentation.
+
+![NERDTree Screenshot](https://github.com/scrooloose/nerdtree/raw/master/screenshot.png)
+
+Installation
+------------
+
+#### [pathogen.vim](https://github.com/tpope/vim-pathogen)
+
+    git clone https://github.com/scrooloose/nerdtree.git ~/.vim/bundle/nerdtree
+
+Then reload Vim, run `:helptags ~/.vim/bundle/nerdtree/doc/` or `:Helptags`, and check out `:help NERDTree.txt`.
+
+
+#### [apt-vim](https://github.com/egalpin/apt-vim)
+
+    apt-vim install -y https://github.com/scrooloose/nerdtree.git
+
+F.A.Q.
+------
+
+> Is there any support for `git` flags?
+
+Yes, install [nerdtree-git-plugin](https://github.com/Xuyuanp/nerdtree-git-plugin).
+
+---
+
+> Can I have the nerdtree on every tab automatically?
+
+Nope. If this is something you want then chances are you aren't using tabs and
+buffers as they were intended to be used. Read this
+http://stackoverflow.com/questions/102384/using-vims-tabs-like-buffers
+
+If you are interested in this behaviour then consider [vim-nerdtree-tabs](https://github.com/jistr/vim-nerdtree-tabs)
+
+---
+> How can I open a NERDTree automatically when vim starts up?
+
+Stick this in your vimrc: `autocmd vimenter * NERDTree`
+
+---
+> How can I open a NERDTree automatically when vim starts up if no files were specified?
+
+Stick this in your vimrc:
+
+    autocmd StdinReadPre * let s:std_in=1
+    autocmd VimEnter * if argc() == 0 && !exists("s:std_in") | NERDTree | endif
+
+Note: Now start vim with plain `vim`, not `vim .`
+
+---
+> How can I open NERDTree automatically when vim starts up on opening a directory?
+
+    autocmd StdinReadPre * let s:std_in=1
+    autocmd VimEnter * if argc() == 1 && isdirectory(argv()[0]) && !exists("s:std_in") | exe 'NERDTree' argv()[0] | wincmd p | ene | endif
+
+This window is tab-specific, meaning it's used by all windows in the tab. This trick also prevents NERDTree from hiding when first selecting a file.
+
+---
+> How can I map a specific key or shortcut to open NERDTree?
+
+Stick this in your vimrc to open NERDTree with `Ctrl+n` (you can set whatever key you want):
+
+    map <C-n> :NERDTreeToggle<CR>
+
+---
+> How can I close vim if the only window left open is a NERDTree?
+
+Stick this in your vimrc:
+
+    autocmd bufenter * if (winnr("$") == 1 && exists("b:NERDTree") && b:NERDTree.isTabTree()) | q | endif
+
+---
+> Can I have different highlighting for different file extensions?
+
+See here: https://github.com/scrooloose/nerdtree/issues/433#issuecomment-92590696
+
+---
+> How can I change default arrows?
+
+Use these variables in your vimrc. Note that below are default arrow symbols
+
+    let g:NERDTreeDirArrowExpandable = '▸'
+    let g:NERDTreeDirArrowCollapsible = '▾'