Document Codex usage

README.md

@@ -189,3 +189,21 @@ If `psql` cannot connect, verify that PostgreSQL is listening locally and that t
 - Project documentation is written in English.
 - Code comments are written in English.
 - User-facing chat responses for this project should be in Czech unless the user asks otherwise.
+
+## Codex
+
+Use Codex from the repository root so it can read `README.md`, `AGENTS.md`, and the local project files.
+
+Start a new Codex session:
+
+```bash
+npx @openai/codex --no-alt-screen -s workspace-write
+```
+
+Resume an existing Codex session:
+
+```bash
+npx @openai/codex resume <session-id> --no-alt-screen -s workspace-write
+```
+
+For repository-specific agent behavior, see `AGENTS.md`.