docs: describe atproto-backed /pub route

README.md

@@ -18,3 +18,15 @@ pnpm build        # build for production
 pnpm preview      # preview the production build on port 5050
 pnpm typecheck    # run vue-tsc
 ```
+
+## AT Protocol notes (`/pub`)
+
+Pages under `/pub/:rkey/:slug` are generated at build time from records
+published to my AT Protocol repository.
+
+- DID: `did:plc:4m3kouplb7s7xozjd3whinvl`
+- Collection: `site.standard.document`
+- PDS endpoint is resolved via [plc.directory](https://plc.directory),
+  then records are listed with `com.atproto.repo.listRecords`.
+
+See `src/api/fetch-notes.ts` and `src/pages/pub/[rkey]/[slug].vue`.