add install instructions

This resolves #144.

Author: ap

README.md

@@ -3,6 +3,12 @@
 <div align="center">
 A very fast, multi-syntax context-sensitive color name highlighter<br>
 <img src="https://raw.githubusercontent.com/ap/vim-css-color/5377c65022ee6d660b898bad954aeea73fa613b8/screenshot.png" width="763">
+
+<sub>
+<pre><code>#  <b>Install</b>:  If you use a plugin manager then follow its instructions.  Otherwise:       
+git clone https://github.com/ap/vim-css-color.git ~/.vim/pack/default/start/vim-css-color</code></pre>
+</sub><br>
+
 </div>
 
 <sub>Inspired