chore(docs): update TOC

Author: 0xBAMA

readme.md

@@ -49,6 +49,8 @@ A hand-picked list of graphics programming resources maintained by graphics prog
   - [Software Rasterization](#software-rasterization)
 - [Graphics Effects](#graphics-effects)
   - [Normal Mapping](#normal-mapping)
+  - [Hash Functions](#hash-functions)
+  - [Dithering](#dithering)
   - [Shadow](#shadow)
   - [Ambient Occlusion](#ambient-occlusion)
   - [Reflection](#reflection)
@@ -59,7 +61,7 @@ A hand-picked list of graphics programming resources maintained by graphics prog
   - [Tessellation](#tessellation)
   - [Voxel Rendering](#voxel-rendering)
   - [Volume Rendering](#volume-rendering)
-  - [Dithering](#dithering)
+  - [Dithering](#dithering-1)
   - [Sprite Rendering](#sprite-rendering)
   - [Atmosphere Scattering](#atmosphere-scattering)
   - [Grass Rendering](#grass-rendering)