Add package: Silent's Cel Shading Shader

[s-ilent]

Package submission

Add this entry to src/BasisPM.Server/seed/packages.json:

{
  "id": "com.s-ilent.crosstone",
  "name": "Silent's Cel Shading Shader",
  "description": "Unity shaders for cel/toon shading. Designed to take Unity's HDR lighting into account while presenting materials in the best possible way.",
  "author": "Silent",
  "category": "Shaders",
  "tags": [
    "tools",
    "editor",
    "shader",
    "material"
  ],
  "source": "community",
  "gitUrl": "https://gitlab.com/s-ilent/SCSS.git",
  "repoUrl": "https://gitlab.com/s-ilent/SCSS",
  "image": null,
  "unity": "6000.4",
  "version": "1.2.0",
  "basisVersion": "main",
  "license": "MIT",
  "discord": "https://discord.gg/7x3fNpfh6f",
  "donate": null,
  "link": null
}