Update Readme.md

docs/Readme.md

@@ -9,6 +9,7 @@ Documents
 * [Parameters Tuning](./Parameters-tuning.md)
 * [Python API Reference](./Python-API.md)
 * [Parallel Learning Guide](https://github.com/Microsoft/LightGBM/wiki/Parallel-Learning-Guide)
+* [GPU Tutorial](./GPU-Tutorial.md)
 * [FAQ](./FAQ.md)
 * [Development Guide](./development.md)