Adding install instructions

Author: Murilo Marinho

docs/README.md

@@ -2,8 +2,18 @@
 
 ## Quickstart
 
+### Set up PPA (do only once)
+
+```commandline
+curl -s --compressed "https://smartarmstack.github.io/smart_arm_stack_ros2/KEY.gpg" | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/smartarmstack_lgpl.gpg >/dev/null
+sudo curl -s --compressed -o /etc/apt/sources.list.d/smartarmstack_lgpl.list "https://smartarmstack.github.io/smart_arm_stack_ros2/smartarmstack_lgpl.list"
+sudo apt update
+```
+
+### Installation (do only once)
+
 ```commandline
-TODO
+sudo apt-get install ros-jazzy-sas-*
 ```
 
 ## A quick note