[chore] update app server doc with skills

codex-rs/app-server/README.md

@@ -11,6 +11,8 @@
 - [Initialization](#initialization)
 - [API Overview](#api-overview)
 - [Events](#events)
+- [Approvals](#approvals)
+- [Skills](#skills)
 - [Auth endpoints](#auth-endpoints)
 
 ## Protocol
@@ -196,6 +198,25 @@ You can optionally specify config overrides on the new turn. If specified, these
 } } }
 ```
 
+### Example: Start a turn (invoke a skill)
+
+Invoke a skill by sending a text input that begins with `$<skill-name>`.
+
+```json
+{ "method": "turn/start", "id": 33, "params": {
+    "threadId": "thr_123",
+    "input": [
+        { "type": "text", "text": "$skill-creator Add a new skill for triaging flaky CI and include step-by-step usage." }
+    ]
+} }
+{ "id": 33, "result": { "turn": {
+    "id": "turn_457",
+    "status": "inProgress",
+    "items": [],
+    "error": null
+} } }
+```
+
 ### Example: Interrupt an active turn
 
 You can cancel a running Turn with `turn/interrupt`.
@@ -405,6 +426,30 @@ Order of messages:
 
 UI guidance for IDEs: surface an approval dialog as soon as the request arrives. The turn will proceed after the server receives a response to the approval request. The terminal `item/completed` notification will be sent with the appropriate status.
 
+## Skills
+
+Skills are invoked by sending a text input that starts with `$<skill-name>`. The rest of the text is passed to the skill as its input.
+
+Example:
+
+```
+$skill-creator Add a new skill for triaging flaky CI and include step-by-step usage.
+```
+
+Use `skills/list` to fetch the available skills (optionally scoped by `cwd` and/or with `forceReload`).
+
+```json
+{ "method": "skills/list", "id": 25, "params": {
+    "cwd": "/Users/me/project",
+    "forceReload": false
+} }
+{ "id": 25, "result": {
+    "skills": [
+        { "name": "skill-creator", "description": "Create or update a Codex skill" }
+    ]
+} }
+```
+
 ## Auth endpoints
 
 The JSON-RPC auth/account surface exposes request/response methods plus server-initiated notifications (no `id`). Use these to determine auth state, start or cancel logins, logout, and inspect ChatGPT rate limits.