docs: add window manager guide

README.md

@@ -104,6 +104,28 @@ ln -sf "${THEME_DIR}/gtk-4.0/gtk-dark.css" "${HOME}/.config/gtk-4.0/gtk-dark.css
   ```
 3. For a more in depth tutorial see Hamza Algohary's tutorial on [It's FOSS](https://itsfoss.com/flatpak-app-apply-theme/)
 
+### Handling GTK theme installation from window manager
+
+1. Install unzip and curl.
+2. Go to your window manager config file.
+3. Add an entrance to the config file to be executed when your window manager is loaded.
+    - i3/sway example:
+    ```
+    # catppuccin
+    set $ctp-version v0.6.1
+    exec_always if [ ! -e ~/.themes/Catppuccin-Frappe-Standard-Lavender-dark ]; then \
+      mkdir -p ~/.themes \
+      && curl -L https://github.com/catppuccin/gtk/releases/download/$ctp-version/Catppuccin-Frappe-Standard-Lavender-dark.zip -o ~/.themes/catppuccin.zip \
+      && unzip ~/.themes/catppuccin.zip -d ~/.themes/ \
+      && rm -rf ~/.themes/catppuccin.zip; fi
+    ```
+    >Note: The previous example execute that script every time i3/sway is reloaded.
+4. Set the GTK_THEME environment variable:
+```sh
+export GTK_THEME='Catppuccin-Frappe-Standard-Lavender-dark:dark'
+```
+>Note: In order to update the theme's version, just change the variable `$ctp-version`.
+
 ### Using the script
 
 **Note**: Ensure that you have at least Python version 3.10 installed