doc: add new minimalistic theme inspired by material ui

Author: lifejuggler

README.md

@@ -99,11 +99,11 @@ Using the `theme` prop along with an imported theme module, you can easily overr
 
 ### Featured themes
 
-|                 ![File Explorer Theme](https://user-images.githubusercontent.com/4413963/32144502-1df1ae08-bcfd-11e7-8f63-8b836dace1a4.png)                  |     <img alt="Full Node Drag Theme" src="https://user-images.githubusercontent.com/4413963/33521792-61dc2c50-d81f-11e7-8ab1-359661a11ca4.png" width="300">     |
-| :----------------------------------------------------------------------------------------------------------------------------------------------------------: | :------------------------------------------------------------------------------------------------------------------------------------------------------------: |
-|                                                                      **File Explorer**                                                                       |                                                                       **Full Node Drag**                                                                       |
-|                                                           react-sortable-tree-theme-file-explorer                                                            |                                                            react-sortable-tree-theme-full-node-drag                                                            |
-| [Github](https://github.com/fritz-c/react-sortable-tree-theme-file-explorer) \| [NPM](https://www.npmjs.com/package/react-sortable-tree-theme-file-explorer) | [Github](https://github.com/fritz-c/react-sortable-tree-theme-full-node-drag) \| [NPM](https://www.npmjs.com/package/react-sortable-tree-theme-full-node-drag) |
+|                 ![File Explorer Theme](https://user-images.githubusercontent.com/4413963/32144502-1df1ae08-bcfd-11e7-8f63-8b836dace1a4.png)                  |     <img alt="Full Node Drag Theme" src="https://user-images.githubusercontent.com/4413963/33521792-61dc2c50-d81f-11e7-8ab1-359661a11ca4.png" width="300">     |     <img alt="MINIMAL THEME" src="https://github.com/lifejuggler/react-sortable-tree-theme-minimal/blob/master/example-resource/main.png" width="300">     |
+| :----------------------------------------------------------------------------------------------------------------------------------------------------------: | :------------------------------------------------------------------------------------------------------------------------------------------------------------: | :--------------------------------------------------------------------------------------------------------------------------------------------------------: |
+|                                                                      **File Explorer**                                                                       |                                                                       **Full Node Drag**                                                                       |                                                       **Minimalistic theme inspired from MATERIAL UI**                                                     |
+|                                                           react-sortable-tree-theme-file-explorer                                                            |                                                            react-sortable-tree-theme-full-node-drag                                                            |                                                              react-sortable-tree-theme-minimal                                                             |
+| [Github](https://github.com/fritz-c/react-sortable-tree-theme-file-explorer) \| [NPM](https://www.npmjs.com/package/react-sortable-tree-theme-file-explorer) | [Github](https://github.com/fritz-c/react-sortable-tree-theme-full-node-drag) \| [NPM](https://www.npmjs.com/package/react-sortable-tree-theme-full-node-drag) |    [Github](https://github.com/lifejuggler/react-sortable-tree-theme-minimal) \| [NPM](https://www.npmjs.com/package/react-sortable-tree-theme-minimal)    |
 
 **Help Wanted** - As the themes feature has just been enabled, there are very few (only _two_ at the time of this writing) theme modules available. If you've customized the appearance of your tree to be especially cool or easy to use, I would be happy to feature it in this readme with a link to the Github repo and NPM page if you convert it to a theme. You can use my [file explorer theme repo](https://github.com/fritz-c/react-sortable-tree-theme-file-explorer) as a template to plug in your own stuff.