Add skin variations

Author: mmistakes

README.md

@@ -104,7 +104,10 @@ one of the following to your [`/_data/theme.yml`](_data/theme.yml) file:
 
 |                 |               |               |
 | --------------- | ------------- | ------------- |
+| ![default-skin](https://cloud.githubusercontent.com/assets/1376749/24115744/c0618c90-0d7a-11e7-8e2d-ec70f9db0c1b.png) | ![night-skin](https://cloud.githubusercontent.com/assets/1376749/24115770/d61127f8-0d7a-11e7-9158-986bee2be8e7.png) | ![plum-skin](https://cloud.githubusercontent.com/assets/1376749/24115778/db523a0e-0d7a-11e7-9452-8692b736d67e.png) |
 | `skin: default` | `skin: night` | `skin: plum`  |
+| ![sea-skin](https://cloud.githubusercontent.com/assets/1376749/24115788/e27d818a-0d7a-11e7-8c56-2480e9ae83fb.png) | ![soft-skin](https://cloud.githubusercontent.com/assets/1376749/24115790/e6e548e8-0d7a-11e7-8e2d-d8053e8befd1.png)
+ | ![steel-skin](https://cloud.githubusercontent.com/assets/1376749/24115799/eb2108e8-0d7a-11e7-8cc3-a6f22e4082ee.png) |
 | `skin: sea`     | `skin: soft`  | `skin: steel` |
 
 ### Google Fonts