Update README.md

Author: dragen1860

README.md

@@ -21,6 +21,9 @@ pip install tensorflow==2.0.0-alpha0
 ```
 
 2. GPU install
+
+Install `CUDA 10.0`(or after) and `cudnn` by yourself. and set `LD_LIBRARY_PATH` up.
+
 ```python
 pip install tensorflow-gpu==2.0.0-alpha0
 ```