docs: slim down README and split build/usage docs into docs/. Targetted .md files.

Author: alan-george-lk

DEPENDENCIES.md

@@ -254,6 +254,6 @@ To verify you have all dependencies linked correctly:
 
 ## Need Help?
 
-- See `README_BUILD.md` for complete build instructions
+- See [`docs/building.md`](docs/building.md) for complete build instructions
 - Check `CMakeLists.txt` lines 287-381 for the exact CMake configuration
 - Open an issue at: https://github.com/livekit/client-sdk-cpp/issues

README.md

@@ -0,0 +1,14 @@
+# Repository Documentation
+
+Additional documentation for the SDK.
+
+- [Building](building.md) — prerequisites, build scripts, CMake presets,
+  vcpkg, Docker, integration into your CMake project, troubleshooting.
+- [Logging](logging.md) — compile-time vs runtime filtering, log levels,
+  custom sinks (file, JSON, ROS2 `RCLCPP_*` macros).
+- [Tracing](tracing.md) — Chromium-format performance traces, viewing in
+  `chrome://tracing` and Perfetto.
+- [Testing](testing.md) — unit, integration, and stress test suites; env
+  vars; token-helper script for local `livekit-server --dev` runs.
+- [Developer tools](tools.md) — `clang-tidy`, `clang-format`, `valgrind`,
+  Doxygen, pre-commit hook, Rust submodule recovery tips.