feat: Add environment variables example

- Add .env.example with common configuration options
- Include API, app, and feature flag examples

Author: ishansasika

.env.example

@@ -0,0 +1,16 @@
+# API Configuration
+NG_APP_API_URL=https://api.example.com
+NG_APP_API_KEY=your_api_key_here
+
+# App Configuration
+NG_APP_NAME=Angular Tailwind Template
+NG_APP_VERSION=1.0.0
+
+# Feature Flags
+NG_APP_ENABLE_ANALYTICS=false
+NG_APP_ENABLE_DEBUG=false
+
+# Firebase (if using)
+# NG_APP_FIREBASE_API_KEY=
+# NG_APP_FIREBASE_AUTH_DOMAIN=
+# NG_APP_FIREBASE_PROJECT_ID=