message: add description to schema-extract package.json
diff: {
  "name": "@stylable/schema-extract",
  "version": "0.1.1",
  + "description": "A utility for extracting JSON schema objects from Stylable stylesheets",
  "main": "cjs/index.js",
  "module": "esm/index.js",
  "types": "esm/index.d.ts",
  },
  "license": "BSD-3-Clause",
  "repository": "https://github.com/wix/stylable/tree/master/packages/schema-extract",
  - "sideEffects": false
  + "sideEffects": false,
  + "author": "Wix.com"
  }
  