added example command for replacing packages

README.md

@@ -1,3 +1,13 @@
 # alhp
 
 Build script for archlinux instructionset enabled repos.
+
+## Replace packages
+Following command reinstalls all packages found in the repo **extra-znver2** that are already installed.
+Replace `extra-znver2` with whatever repo you want to install.
+
+```shell script
+pacman -S $(pacman -Sl extra-znver2 | grep installed | cut -f 2 -d " " | perl -p -i -e 's/\R/ /g;')
+```
+
+This is only needed once, new updates are coming from this new repo then, as usual.