Refactor: Use .env for admin credentials

.env.example

@@ -1,6 +1,19 @@
-# Timezone
-TZ=Europe/Copenhagen
+# Docker WebUI Configuration
+# Copy this file to .env and customize your settings
+
+# ===============================================
+# ADMIN CREDENTIALS
+# ===============================================
+# IMPORTANT: Change these before first run!
+# These credentials are used to create the admin account
 
-# Admin Credentials (CHANGE THESE!)
 ADMIN_EMAIL=admin@docker-webui.local
 ADMIN_PASSWORD=changeme123
+
+# ===============================================
+# TIMEZONE
+# ===============================================
+# Set your server timezone
+# Examples: Europe/Copenhagen, America/New_York, Asia/Tokyo
+
+TZ=Europe/Copenhagen