docs(readme): add configuration table and forwarding notes

README.md

@@ -1,6 +1,6 @@
 # forward-telegram-message
 
-Forward Telegram messages between chats automatically.
+Mirror Telegram messages between two chats using Telethon — runs as a user-account, not a bot.
 
 ## Quick start
 
@@ -13,6 +13,23 @@ python main.py
 
 Get `API_ID` and `API_HASH` from [my.telegram.org](https://my.telegram.org).
 
+## Configuration
+
+| Variable | Required | Description |
+|----------|----------|-------------|
+| `PHONE` | Yes | Your Telegram phone number (e.g. `+84912345678`) |
+| `API_ID` | Yes | App API ID from my.telegram.org |
+| `API_HASH` | Yes | App API hash from my.telegram.org |
+| `SOURCE_GROUP_ID` | Yes | ID of the source chat/group to mirror from |
+| `TARGET_GROUP_ID` | Yes | ID of the destination chat/group to forward into |
+
+## Notes
+
+- Runs as a **user account** (Telethon), not a bot — requires first-time interactive login to generate a session file.
+- Forwards both text messages and media (photos, documents, videos).
+- Re-uses the session file on subsequent runs; no re-auth needed.
+- `SOURCE_GROUP_ID` and `TARGET_GROUP_ID` can be negative (supergroup IDs) or positive (private chat IDs).
+
 ## License
 
 Apache-2.0 — see [LICENSE](LICENSE).