Add prepare script (#3)

Author: mnemitz

package.json

@@ -5,6 +5,7 @@
   "types": "./build/index.d.ts",
   "scripts": {
     "build": "tsc --project tsconfig.json",
+    "prepare": "npm run build",
     "typecheck": "tsc --project tsconfig.json --noEmit",
     "lint": "eslint --ext .ts,.tsx src/",
     "test": "jest --config=config/jest.config.ts --passWithNoTests",