Add install instructions

Author: biotinker

README.md

@@ -7,3 +7,10 @@ This is a fork of the `gpio` app built into the flipper, with added functionalit
 Supports pulling high or low.
 
 Does not (yet) support analog reads.
+
+Installation instructions (Linux):
+
+ - Clone the following repo: https://github.com/flipperdevices/flipperzero-firmware
+ - Clone this repo into flipperzero-firmware/applications_user
+ - Plug in your FlipperZero
+ - Run `./fbt launch_app APPSRC=flipperzero-gpioreader` from within the flipperzero-firmware folder