docs: update Vietnamese input setup instructions in README

Add fcitx5-configtool addon and clarify that Unikey must be added via
fcitx5-configtool's Input Method tab, not through KDE Virtual Keyboard settings.

README.md

@@ -20,7 +20,7 @@ nixos-config/
 
 - **KDE Plasma 6** on Wayland via SDDM
 - **Vietnamese input** via fcitx5 + unikey (Telex/VNI)
-  - After switching, go to System Settings → Virtual Keyboard → select "Fcitx 5"
+  - Open `fcitx5-configtool` → Input Method tab → add **Unikey**
 - **Locale**: English UI, Vietnamese formats (currency, time, etc.), Asia/Ho_Chi_Minh timezone
 - **Pipewire** for audio
 - **Packages**: firefox, kate, claude-code, git
@@ -85,10 +85,8 @@ Commit the resulting `flake.lock` so future rebuilds use the exact same package
 ## Vietnamese input setup (fcitx5)
 
 After first build:
-1. Go to **System Settings → Input Devices → Virtual Keyboard**
-2. Select **Fcitx 5** and apply
-3. In the system tray, right-click the fcitx5 icon → **Configure**
-4. Add **Unikey** as an input method
-5. Switch between English/Vietnamese with **Super+Space**
+1. Open **fcitx5-configtool**
+2. Go to the **Input Method** tab → add **Unikey**
+3. Switch between English/Vietnamese with **Super+Space**
 
 Unikey supports both **Telex** (default) and **VNI** — configure in the Unikey settings.