docs(plugins): point to the example plugin repo and the API 4+ fingerprint

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/README.md

@@ -23,10 +23,13 @@ Requirements for the linked repo:
 - Builds a `cdylib` against [`ocs_plugin_api`](../crates/ocs_plugin_api) and
   exports the host symbols via `ocs_plugin_api::export_plugin!`.
 - Publishes per-platform binaries plus `plugin.toml` as **GitHub Release**
-  assets (see `crates/ocs_example_plugin` and its release workflow for a
-  template). Asset names carry the platform, e.g.
+  assets (see [opencad-example-plugin](https://github.com/HakanSeven12/opencad-example-plugin)
+  and its release workflow for a template). Asset names carry the platform, e.g.
   `your.plugin-linux-x86_64.so`, `…-windows-x86_64.dll`, `…-macos-aarch64.dylib`.
-- `plugin.toml` declares an `api_version` compatible with the host.
+- `plugin.toml` declares an `api_version` compatible with the host (3 or
+  newer). From API 4 on it must also carry the `rustc_version` and
+  `acadrust_source` the library was built with; the host loads it only when
+  both match its own build.
 
 The host reads the release matching the user's platform, checks the API
 version, and installs it into the user's plugins folder.