docs: make the buffered methods clear in reference

Co-authored-by: Michael Brooks <mbrooks@slack-corp.com>

Author: zimeg

slack_sdk/web/client.py

@@ -2946,7 +2946,7 @@ def chat_stream(
           [Reference](https://docs.slack.dev/reference/methods/chat.stopStream).
 
         Args:
-            buffer_size: The length of markdown_text to buffer in-memory before calling a method. Increasing this value
+            buffer_size: The length of markdown_text to buffer in-memory before calling a stream method. Increasing this value
               decreases the number of method calls made for the same amount of text, which is useful to avoid rate limits.
               Default: 256.
             channel: An encoded ID that represents a channel, private group, or DM.