Update Readme and app compile_mcu script

README.org

@@ -25,4 +25,24 @@
   cat /dev/ttyACM0
 #+END_SRC
 
-   If you get a /Permission denied/, try running the command as a superuser (e.g. *sudo*) 
+   If you get a /Permission denied/, you have to add your user to the group of the serial port (in this case /dev/ttyACM0).
+   
+   To check the group of the device:
+
+#+BEGIN_SRC sh
+  ls -la /dev/ttyACM0
+#+END_SRC
+
+   Then add your user to the group (in this case the group is dialout and the user is user)
+
+#+BEGIN_SRC sh
+  sudo usermod -aG dialout user
+#+END_SRC
+
+** ESP8266
+   
+   During the *Week 4*, we used the NodeMCU instead of the Arduino uno, in this case to compile and upload the sketch (in this case we'll use the sketch Test):
+
+#+BEGIN_SRC sh
+  ./compile_mcu.sh Test
+#+END_SRC

compile_mcu.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+if [ $# -lt 1 ]; then
+    echo "Usage: compile.sh <Project>"
+fi
+
+project=$1
+
+arduino-cli compile --fqbn esp8266:esp8266:nodemcuv2 "$project" && arduino-cli upload -p /dev/ttyUSB0 --fqbn esp8266:esp8266:nodemcuv2 "$project"