docs: Update arch_install.md

.dotfiles/arch_install.md

@@ -188,7 +188,7 @@ Set and generate locale
 
 ```console
 # echo LANG=en_US.UTF-8 > /etc/locale.conf
-# sed -i 's/^#en_US.UTF-8 UTF-8/en_US.UTF-8 UTF-8/' /etc/locale.gen
+# sed -i -e 's/^#en_US.UTF-8 UTF-8/en_US.UTF-8 UTF-8/' -e 's/^#de_DE.UTF-8 UTF-8/de_DE.UTF-8 UTF-8/' /etc/locale.gen
 # locale-gen
 ```
 
@@ -327,3 +327,46 @@ Install various packages from dotfiles
 ```console
 $ sudo pacman -S --needed - < $HOME/.dotfiles/pkglist.txt
 ```
+
+Update system just to be sure
+
+```console
+$ sudo pacman -Syu
+```
+
+### AUR
+
+Install `paru` as AUR helper
+
+```console
+$ sudo pacman -S --needed base-devel
+$ git clone https://aur.archlinux.org/paru.git
+$ cd paru
+$ makepkg -si
+```
+
+Install packages from AUR
+
+```console
+$ paru -Sa wlogout
+```
+
+### Flatpak
+
+Install flatpak package
+
+```console
+$ sudo pacman -S flatpak
+```
+
+Add the flathub repo
+
+```console
+$ flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
+```
+
+Install `Flatseal` to manage flatpak permissions via GUI
+
+```console
+$ flatpak install flathub com.github.tchx84.Flatseal
+```