docs: document /tg_info command

docs/telegram-usage.md

@@ -45,15 +45,22 @@ Get your "Id", you will use it for the config parameter `chat_id`.
 
 #### Use Group id
 
-You can use bots in telegram groups by just adding them to the group. You can find the group id by first adding a [RawDataBot](https://telegram.me/rawdatabot) to your group. The Group id is shown as id in the `"chat"` section, which the RawDataBot will send to you:
+To get the group ID, you can add the bot to the group, start freqtrade, and issue a `/tg_info` command.
+This will return the group id to you, without having to use some random bot.
+While "chat_id" is still required, it doesn't need to be set to this particular group id for this command.
+
+The response will also contain the "topic_id" if necessary - both in a format ready to copy/paste into your configuration.
 
 ``` json
-"chat":{
+ {
-   "id":-1001332619709
+    "enabled": true,
+    "token": "********",
+    "chat_id": "-1002403829695",
+    "topic_id": "122"
 }
 ```
 
-For the Freqtrade configuration, you can then use the full value (including `-` if it's there) as string:
+For the Freqtrade configuration, you can then use the full value (including `-` ) as string:
 
 ```json
    "chat_id": "-1001332619709"
@@ -72,6 +79,7 @@ Without this, the bot will always respond to the general channel in the group if
    "topic_id": "3"
 ```
 
+Similar to the group-id - you can use `/tg_info` from the topic/thread to get the correct topic-id.
 
 ## Control telegram noise