Add pip -U

README.md

@@ -460,7 +460,7 @@ PlatformIO will be necessary if we want to flash program to microcontrollers con
 Note that we do not recommend building directly microcontrollers programs on the Raspberry Pi, as it can be pretty slow compared to a regular computer. To tackle this issue, you can use the `pio remote agent` to build locally on your computer, and just delegate the work of flashing the program on the microcontrollers to the Raspberry Pi.
 
 ```sh
-yes | pip install platformio
+yes | pip install -U platformio
 
 # Install udev rules
 sudo curl -s https://raw.githubusercontent.com/platformio/platformio-core/master/scripts/99-platformio-udev.rules -o /etc/udev/rules.d/99-platformio-udev.rules