Add guideline info

Author: williamd1k0

README.md

@@ -8,10 +8,7 @@ HD Designer: 幼幼保护协会 @Coolapk
 
 Pixel Art Designer: [@williamd1k0](https://github.com/williamd1k0/)
 
+Icon guidelines: [Creating a Pixelart Icon Pack - Tumeo Space](https://tumeo.space/blogs/2019/03/11/pixelart-icons/)
+
 ![All icons](assets/dev/all.png)
 ![All icons upscale](assets/dev/all-xxl.png)
-
-
->TODO: Remove unusual icons and wallpapers from MBE Style.
-
->TODO: Write a style guideline doc.