improved docs

Author: rohitcoder

readme.md

@@ -386,6 +386,7 @@ sources:
       token: xoxp-XXXXXXXXXXXXXXXXXXXXXXXXX
       archived_channels: True ## By default False, set to True if you want to scan archived channels also
       limit_mins: 15 ## By default 60 mins
+      limit_from: last_message ## By default current Unix timestamp, available options - UNIX Timestamp (e..g: 1737354387 last_message
       channel_ids:
       - XXXXXXXX
 ```