Edit the README file

Two key changes were made:

 1. A screenshot was added for visual appeal.
 2. The massive (and noisy) feature list was removed. This
    information is adequately covered in the docs.

Fixes #573.

README.markdown

@@ -1,56 +1,16 @@
 The NERDTree
 =============
 
-Intro
------
+Introduction
+------------
 
-The NERD tree allows you to explore your filesystem and to open files and
-directories. It presents the filesystem to you in the form of a tree which you
-manipulate with the keyboard and/or mouse. It also allows you to perform
-simple filesystem operations.
+The NERDTree is a file system explorer for the Vim editor. Using this plugin,
+you 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 other NERDTree features is described in the included documentation.
 
-The following features and functionality are provided by the NERD tree:
-
-  * Files and directories are displayed in a hierarchical tree structure
-  * Different highlighting is provided for the following types of nodes:
-    * files
-    * directories
-    * sym-links
-    * windows .lnk files
-    * read-only files
-    * executable files
-  * Many (customisable) mappings are provided to manipulate the tree:
-    * Mappings to open/close/explore directory nodes
-    * Mappings to open files in new/existing windows/tabs
-    * Mappings to change the current root of the tree
-    * Mappings to navigate around the tree
-    * ...
-  * Directories and files can be bookmarked.
-  * Most NERD tree navigation can also be done with the mouse
-  * Filtering of tree content (can be toggled at runtime)
-    * custom file filters to prevent e.g. vim backup files being displayed
-    * optional displaying of hidden files (. files)
-    * files can be "turned off" so that only directories are displayed
-  * The position and size of the NERD tree window can be customised
-  * The order in which the nodes in the tree are listed can be customised.
-  * A model of your filesystem is created/maintained as you explore it. This
-    has several advantages:
-    * All filesystem information is cached and is only re-read on demand
-    * If you revisit a part of the tree that you left earlier in your
-      session, the directory nodes will be opened/closed as you left them
-  * The script remembers the cursor position and window position in the NERD
-    tree so you can toggle it off (or just close the tree window) and then
-    reopen it (with NERDTreeToggle) the NERD tree window will appear exactly
-    as you left it
-  * You can have a separate NERD tree for each tab, share trees across tabs,
-    or a mix of both.
-  * By default the script overrides the default file browser (netrw), so if
-    you :edit a directory a (slightly modified) NERD tree will appear in the
-    current window
-  * A programmable menu system is provided (simulates right clicking on a node)
-    * one default menu plugin is provided to perform basic filesystem
-      operations (create/delete/move/copy files/directories)
-  * There's an API for adding your own keymappings
+![NERDTree Screenshot](https://github.com/scrooloose/nerdtree/raw/master/screenshot.png)
 
 Installation
 ------------
@@ -66,10 +26,8 @@ Then reload Vim, run `:helptags ~/.vim/bundle/nerdtree/doc/`, and check out `:he
 
     apt-vim install -y https://github.com/scrooloose/nerdtree.git
 
-
-
-Faq
----
+F.A.Q.
+------
 
 > Is there any support for `git` flags?