docs: adding poster to assets (#228)

* docs: adding poster to assets

* readme: fix poster image

README.md

@@ -1,6 +1,6 @@
 [![npm version](https://img.shields.io/npm/v/bknd.svg)](https://npmjs.org/package/bknd)
 
-![bknd](https://raw.githubusercontent.com/bknd-io/bknd/refs/heads/main/docs/_assets/poster.png)
+![bknd](https://raw.githubusercontent.com/bknd-io/bknd/refs/heads/main/docs/public/assets/poster.png)
 
 <p align="center" width="100%">
 <a href="https://stackblitz.com/github/bknd-io/bknd-examples?hideExplorer=1&embed=1&view=preview&startScript=example-admin-rich&initialPath=%2Fdata%2Fschema" target="_blank">