message: docs: remove dev build instructions
diff: <!--email_off-->
  -[Unpkg.com](https://unpkg.com) provides npm-based CDN links. The above link will always point to the latest release on npm. You can also use a specific version/tag via URLs like `https://unpkg.com/vue-router@3.0.0/dist/vue-router.js`.
  +[Unpkg.com](https://unpkg.com) provides npm-based CDN links. The above link will always point to the latest release on npm. You can also use a specific version/tag via URLs like `https://unpkg.com/vue-router@4.0.5/dist/vue-router.global.js`.
  <!--/email_off-->
  npm install vue-router@4
  ```
  -## Dev Build
  -
  -You will have to clone directly from GitHub and build `vue-router` yourself if
  -you want to use the latest dev build.
  +## yarn
  ```bash
  -git clone https://github.com/vuejs/vue-router.git node_modules/vue-router
  -cd node_modules/vue-router
  -npm install
  -npm run build
  +yarn add vue-router@4
  ```
  