docs: update README for preview launch (#392)

## Summary
- Update development status to reflect preview launch
- Add navigation links for publishing, API docs, and ecosystem vision
- Include announcement blog post link
- Add feedback channels (GitHub discussions and Discord)

Author: domdomegg

README.md

@@ -2,14 +2,11 @@
 
 The MCP registry provides MCP clients with a list of MCP servers, like an app store for MCP servers.
 
-📖 **[Full documentation](./docs)**
+[**📤 Publish my MCP server**](docs/guides/publishing/publish-server.md) | [**⚡️ Live API docs**](https://registry.modelcontextprotocol.io/docs) | [**👀 Ecosystem vision**](docs/explanations/ecosystem-vision.md) | 📖 **[Full documentation](./docs)**
 
 ## Development Status
 
-> [!WARNING]  
-> The registry is under [active development](#development-status). The registry API spec is unstable and the official MCP registry database may be wiped at any time.
-
-**2025-09-04 update**: We're targeting a 'preview' go-live on 8th September. This may still be unstable and not provide durability guarantees, but is a step towards being more solidified. A general availability (GA) release will follow later.
+**2025-09-08 update**: The registry has launched in preview 🎉 ([announcement blog post](https://modelcontextprotocol.io/blog/registry-preview)). While the system is now more stable, this is still a preview release and breaking changes or data resets may occur. A general availability (GA) release will follow later. We'd love your feedback in [GitHub discussions](https://github.com/modelcontextprotocol/registry/discussions/new?category=ideas) or in the [#registry-dev Discord](https://discord.com/channels/1358869848138059966/1369487942862504016) ([joining details here](https://modelcontextprotocol.io/community/communication)).
 
 Current key maintainers:
 - **Adam Jones** (Anthropic) [@domdomegg](https://github.com/domdomegg)