Update readme with install script usage info

README.md

@@ -2,12 +2,13 @@
 
 ![](https://i.imgur.com/XitFbtv.gif)
 
-### Installation
+### Installation / update
 
-1. Get theme archive: `wget https://github.com/shvchk/poly-light/archive/master.zip`
-2. Unpack theme: `unzip master.zip`
-3. Remove theme archive: `rm master.zip`
-4. Create GRUB themes directory: `sudo mkdir -p /boot/grub/themes`
-5. Move theme to GRUB themes directory: `sudo mv poly-light-master /boot/grub/themes/poly-light`
-6. Set `GRUB_THEME=/boot/grub/themes/poly-light/theme.txt` in GRUB config: `sudo nano /etc/default/grub`
-7. Update GRUB: `sudo update-grub`
+1. **Secure way:**
+    - Download install script:  
+    `wget -P /tmp https://github.com/shvchk/poly-light/raw/master/install.sh`
+    - Review install script at `/tmp/install.sh`
+    - Run it: `sh /tmp/install.sh`
+
+2. **Easier, less secure way** — just download and run script:  
+    `wget -O - https://github.com/shvchk/poly-light/raw/master/install.sh | sh`