docs: explain ATProto doc publishing in readme

the readme now explains that zat publishes its own docs as
site.standard.document records - dogfooding the protocol.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[e-mail]>

CHANGELOG.md

···
 # changelog
 
+## 0.1.1
+
+- xrpc client sets `Content-Type: application/json` for POST requests
+- docs published as `site.standard.document` records on tag releases
+
 ## 0.1.0
 
 sync types for firehose consumption:

README.md

···
 # [zat](https://zat.dev)
 
-AT Protocol building blocks for zig. [roadmap](docs/roadmap.md) · [atproto records](https://at-me.zzstoatzz.io/view?handle=zat.dev)
+AT Protocol building blocks for zig. [roadmap](docs/roadmap.md)
+
+<details>
+<summary><strong>this readme lives on ATProto</strong></summary>
+
+zat uses itself to publish these docs as [`site.standard.document`](https://standard.site) records on ATProto. they live in [zat.dev's repository](https://at-me.zzstoatzz.io/view?handle=zat.dev), signed by its DID.
+
+</details>
 
 ## install