update README typo

Author: Shuyang

README.md

@@ -21,7 +21,7 @@ Model Context Protocol (MCP) server for Slack Workspaces. This integration suppo
   - Required inputs:
     - `channel_types` (string): Comma-separated channel types. Allowed values: 'mpim', 'im', 'public_channel', 'private_channel'. Example: 'public_channel,private_channel,im'.
     - `sort` (string): Type of sorting. Allowed values: 'popularity' - sort by number of members/participants in each channel.
-    - `limit` (string, default: 100): Limit of channels to fetch.
+    - `limit` (number, default: 100): Limit of channels to fetch.
     - `cursor` (string): Cursor for pagination. Use the value of the last row and column in the response as next_cursor field returned from the previous request.
   - Returns: List of channels