add Archlinux to installation guide

Riesi · Riesi · commit 72dcc44ab38a · 2020-05-13T13:39:03.000+02:00
diff --git a/README.txt b/README.txt
@@ -11,6 +11,8 @@ INSTALLATION:
 
  - Debian/Ubuntu: 
    apt install arduino python-serial
+ - Archlinux:
+   pacman -S arduino python-pyserial
 
 HOW TO:
 
