docs(README): add concepts, testing, and links

Author: tony

README.md

@@ -86,5 +86,79 @@ right.send_keys("htop", enter=True)
 print(f"Attach with: tmux attach -t {session.name}")
 ```
 
+## Core concepts
+
+| libtmux object | tmux concept                | Notes                          |
+|----------------|-----------------------------|--------------------------------|
+| `Server`       | tmux server / socket        | Entry point; owns sessions     |
+| `Session`      | tmux session (`$0`, `$1`,...) | Owns windows                   |
+| `Window`       | tmux window (`@1`, `@2`,...)  | Owns panes                     |
+| `Pane`         | tmux pane (`%1`, `%2`,...)    | Where commands run             |
+
+Collections are live and queryable:
+
+```python
+server = libtmux.Server()
+session = server.sessions.get(session_name="demo")
+api_windows = session.windows.filter(window_name__startswith="api")
+pane = session.active_window.active_pane
+pane.send_keys("echo 'hello from libtmux'", enter=True)
+```
+
+## tmux vs libtmux vs tmuxp
+
+| Tool    | Layer                      | Typical use case                                   |
+|---------|----------------------------|----------------------------------------------------|
+| tmux    | CLI / terminal multiplexer | Everyday terminal usage, manual control            |
+| libtmux | Python API over tmux       | Programmatic control, automation, testing          |
+| tmuxp   | App on top of libtmux      | Declarative tmux workspaces from YAML / TOML       |
+
+## Raw tmux when you need it
+
+```python
+server = libtmux.Server(socket_name="libtmux_doctest")
+result = server.cmd("display-message", "hello world")
+print(result.stdout)      # ['hello world']
+print(result.returncode)  # 0 on success
+```
+
+## Testing & fixtures
+
+- pytest plugin provides fresh tmux server/session/window/pane fixtures
+- Temporary HOME and tmux config fixtures keep indices stable
+- `TestServer` helper spins up multiple isolated tmux servers
+- See the docs for full fixture list and usage examples
+
+## When you might not need libtmux
+
+- Layouts are static and live entirely in tmux config files
+- You do not need to introspect or control running tmux from other tools
+- Python is unavailable where tmux is running
+
+## Project links
+
+- Docs: [docs]
+- API reference: [api]
+- Changelog: [history]
+- Migration notes: [migration]
+- Issues: [issues]
+- Test coverage: [coverage]
+- Releases: [releases]
+- License: [license]
+- Support: [support]
+
+## Contributing & support
+
+Contributions are welcome. Please open an issue or PR if you find a bug or want to improve the API or docs. If libtmux helps you ship, consider sponsoring development via [support].
+
+[docs]: https://libtmux.git-pull.com
+[api]: https://libtmux.git-pull.com/api.html
+[history]: https://libtmux.git-pull.com/history.html
+[migration]: https://libtmux.git-pull.com/migration.html
+[issues]: https://github.com/tmux-python/libtmux/issues
+[coverage]: https://codecov.io/gh/tmux-python/libtmux
+[releases]: https://pypi.org/project/libtmux/
+[license]: https://github.com/tmux-python/libtmux/blob/master/LICENSE
+[support]: https://tony.sh/support.html
 [tmuxp]: https://tmuxp.git-pull.com
 [tmux]: https://github.com/tmux/tmux