add prebuild step and include assets in package.json build process

package.json

@@ -6,6 +6,7 @@
     "types": "dist/index.d.ts",
     "files": [
         "dist",
+        "dist/assets",
         "README.md",
         "LICENSE"
     ],
@@ -14,7 +15,8 @@
     },
     "scripts": {
         "clean": "rimraf dist",
-        "build": "npm run clean && tsc",
+        "prebuild": "mkdir -p dist/assets",
+        "build": "npm run clean && npm run prebuild && cp src/assets/* dist/assets/ && tsc",
         "publish:local": "npm run build && npm pack",
         "publish:npm": "npm run build && npm publish",
         "version:patch": "npm version patch",
@@ -61,4 +63,4 @@
     "publishConfig": {
         "access": "public"
     }
-}
+}