chore: add Vercel OSS Program badge

Added Vercel OSS Program badge to README.
Signed-off-by: boojack <stevenlgtm@gmail.com>

README.md

@@ -130,4 +130,6 @@ Memos is open-source software licensed under the [MIT License](LICENSE).
 
 **[Website](https://www.usememos.com)** • **[Documentation](https://www.usememos.com/docs)** • **[Demo](https://demo.usememos.com/)** • **[Discord](https://discord.gg/tfPJa4UmAv)** • **[X/Twitter](https://x.com/usememos)**
 
-Made with ❤️ by the Memos community
+<a href="https://vercel.com/oss">
+  <img alt="Vercel OSS Program" src="https://vercel.com/oss/program-badge.svg" />
+</a>