Add note about using CPU-only version of TF

Author: EdjeElectronics

README.md

@@ -114,6 +114,13 @@ Install tensorflow-gpu in this environment by issuing:
 ```
 (tensorflow1) C:\> pip install --ignore-installed --upgrade tensorflow-gpu
 ```
+
+NOTE: You can also use the CPU-only version of TensorFow, but it will run much slower. If you want to use the CPU-only version, just issue:
+
+```
+(tensorflow1) C:\> pip install --ignore-installed --upgrade tensorflow
+```
+
 Install the other necessary packages by issuing the following commands:
 ```
 (tensorflow1) C:\> conda install -c anaconda protobuf