Update pip.md

the command to install pip install tensorflow[and-cuda] is not working. The pip install 'tensorflow[and-cuda]' works.

Author: joaomh

site/en/install/pip.md

@@ -26,7 +26,7 @@ step-by-step instructions.
     for more information about this collaboration.
 
     ```bash
-    python3 -m pip install tensorflow[and-cuda]
+    python3 -m pip install 'tensorflow[and-cuda]'
     # Verify the installation:
     python3 -c "import tensorflow as tf; print(tf.config.list_physical_devices('GPU'))"
     ```